


Mix up at the Lab

by ShadowMelter



Category: Undertale (Video Game)
Genre: Age Difference, Angst, Drug Addiction, Drugs, Dubious Consent, Ecto-Tongue, Gaster is kind of a jerk, Height Kink, Hurt/Comfort, Light Bondage, M/M, Mating Cycles/In Heat, Non-Consensual, Sanster, Science!Sans - Freeform, Sensual Play, Sexual Coercion, Skeleton Heat, Soul Sex, Touching, implied past Kingdings
Language: English
Status: In-Progress
Published: 2016-02-08
Updated: 2016-05-18
Packaged: 2018-05-19 04:54:08
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 12
Words: 34,199
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5954344
Author URL: https://archiveofourown.org/users/ShadowMelter/pseuds/ShadowMelter
Summary: <blockquote class="userstuff">
              <p>Sans accidentally ingests the wrong experimental drug and things get a bit heated. Doctor Gaster is trying his best to remain in control, but he's not about to let his assistant suffer. However, Sans might be the least of Gaster's worries.</p>
            </blockquote>





	1. An Agreement Between Colleagues

**Author's Note:**

> I've never written smut before, but there's a first time for everything!

Sans has been working at the Laboratory for about five months now and during those five months, he has come to learn a thing or two about everyone’s favorite Royal Scientist, Dr. Gaster. The first thing he learned about the man was that he was a freaking genius. Gaster has a unique ability to make connections where there shouldn’t even be connections. For example, there was one time the entire science team was working on solving a complex algorithm that just wasn’t adding up, and by the end of the day the whole team had agreed that the problem was unsolvable. 

Well, the next morning Gaster came in, took one look at it, and solved it in 10 minutes. The ENTIRE science department spent all day on that algorithm and Gaster solved it like it was some kind of easy-peasy word scramble. 

Now, the second thing he learned about Dr. Gaster was that the man was a goddamn idiot. No, seriously. The man was so reckless it would be funny if the implications weren’t so frightening. Gaster completely lacks any common sense when it comes to experimentation. 

He often treats his untested hypotheses as if they are well established substantiated theories. In other words, Gaster somehow convinces himself that his desired outcome for an experiment is the only possible outcome. He wasn’t necessarily arrogant, he was just too optimistic about his own work to see the flaws if that makes any sense. Unfortunately being a genius doesn’t prevent Gaster from making stupid mistakes from time to time. 

Sometimes he gets overeager about a project and forgets to take into account important variables. The results were often unpredictable, and even the most benign experiments have gone horribly wrong because he was simply too impatient. The idiot won’t even wait for proper test subjects! Sometimes he just goes ahead and experiments on himself without telling anyone. 

Apparently a few months before Sans had joined the science team, Gaster had a really bad accident involving one of his experiments. The man almost died but got lucky and only ended up cracking his skull in a few places. Sans didn’t know what the experiment was, but he was pretty damn sure the accident could have been prevented if Gaster weren’t so reckless. 

Sans supposed this was why when he came into the lab this morning, he was entirely unsurprised to find that his boss had once again gotten himself into trouble after a night of self-experimentation.

The moment Sans slid his keycard and opened the door to the lab he knew something was wrong. The lights were on but there was no sign of Gaster. The doctor was always first to the lab in the morning and the last to leave at night so finding the lab completely empty was highly unusual. 

Maybe he was just late today, but why would he leave the lights on last night if that were the case? 

As Sans walked in he spotted something in the middle of the room and gently placed his mug of piping hot coffee down on his desk before strolling over to it.  
It was a pair of glasses. Correction, it was a pair of black glasses with rectangular frames that belonged to Gaster. Sans folded the glasses and put them in the front pocket of his white lab coat for safekeeping. 

Dr. Gaster was never without his glasses. Sans could feel his soul throb with anxiety within his ribcage. There wasn’t any sign of a struggle, so he felt it was pretty safe to assume the doctor has gone and done something stupid again. With an exasperated sigh, he got onto all fours and began searching under the desks for his missing boss.  
Sans was swearing and muttering under his breath as he crawled from desk to desk. “i swear to god if he shrunk himself again i’m gonna shove him into a jar and keep him on my shelf so i ca-“ 

A strange gurgling sound cut him off mid rant. 

Sans quickly got out from under the desk and looked around for the source of the noise. It didn’t take long before he heard it again. It was coming from… above him? He looked up and… oh… oh my god. 

It was Dr. Gaster, and he was curled up on the ceiling fast asleep. The gurgling noise was the sound of him snoring. The man even had his thumb in his mouth, what the hell? That’s freaking _adorable_. 

Sans couldn’t contain his laughter. He was laughing so hard tears were starting to form around his eye sockets. 

The sound of Sans’ laughter echoed around the lab, startling the Royal Scientist out of his surprisingly deep sleep. Gaster ripped his thumb out of his mouth and looked around frantically, squinting until he spotted a small, blurry blob below him. He couldn’t see a damn thing without his glasses but he knew exactly who that laugh belonged to. 

Surprised, he stammered, “S-sans? Th-thank goodness you’re here, help me down!”

Sans managed to stop laughing long enough to say, “hey doc, how’s the weather up there?”

Gaster groaned and felt he face heat up with embarrassment. Why did Sans have to be the one to find him? “Sans, I mean it! I didn’t take into account the high ceiling while I was working on the antigravity belt.” The tall skeleton in the black lab coat pointed to the device strapped around his waist. “This is quite serious, as I’m absolutely certain that if I were to turn it off right now I will plummet to my death.” 

The mention of death instantly caused Sans’ laughter to die in his throat. He wheezed, “w-woah. hang in there doc, i gotcha.” Blue energy erupted out of his left eye socket and he thrust his hand towards the distressed scientist. His magic latched onto Gaster’s soul turning it blue and slowly he pulled the man towards himself. 

When Gaster was firmly on the ground, the tall skeleton pressed the circular button on the belt turning it off. 

“Thank you, Sans, your help was much appreciated.” He walked over to his desk, unhooked the belt from his slender frame and placed it on the metal surface. 

Sans’ magic dissipated and he watched as Gaster sauntered around, acting as if getting stuck to the ceiling all night was only a slight inconvenience. He couldn’t help but feel slightly miffed by Gaster’s lack of concern for his own safety.

“hey, doc? what would have happened to you if that belt ran out of batteries before i could find you?” 

Gaster turned to Sans with a frown on his face and hummed in contemplation. “Well Sans, if the batteries ran out, the belt would have turned off and I would have fallen.” Tapping a finger against his mouth he looked up at the ceiling and said, “Judging by the height at which I was stuck at, I would have either died or been horribly injured upon falling to the ground.” Gaster didn’t look remotely phased by this information as he turned back to examine the belt on his desk. 

Sans was getting angry now. He was too short to reach Gaster’s shoulders so he settled for grabbing the man’s elbow and spun the scientist around so he was facing him once more.

“S-sans? Wha-“

“listen, gaster, you need to stop experimenting on yourself. it would be a travesty if the underground lost such a brilliant mind to a stupid failed experiment, and i really don’t want come in one day to find you dead on the laboratory floor, capiche?” he ended the lecture with a slight growl and clenched his fists tightly to his sides. 

He was glaring at the ground when he felt boney fingers under his chin force his head up. 

Gaster was looking down at him with such concern. Sans could feel his face flush at the intensity of older skeleton’s stare. 

“I had no idea you felt so strongly about my research methods.” Gaster couldn’t help but smirk when he noticed a slight blue blush creep across his assistant’s face. How cute.  
He pulled his hand away from the small skeleton and walked back to his desk where he turned around his chair and sat down so he was facing his assistant. 

“Sans, do you know why I experiment on myself?” 

Sans wrung his small hands together and shook his head. He had no idea why Dr. Gaster insisted on conducting dangerous experiments on himself. He had just assumed the doctor was incredibly confident in his own abilities. 

“I experiment on myself,” Gaster continued, “because I don’t want to put other monsters at risk. If something were to go wrong, I could never forgive myself for placing another monster in such danger. I’d rather risk injury to myself testing a potentially dangerous experiment, than risk injury to a monster test subject.” Gaster was lying. He honestly didn’t care about testing on other monsters, but he knew Sans would only accept a ridiculously noble answer.

Gaster could practically hear the cogs in his assistant’s head turn as he absorbed this information.  
As Sans listened to Dr. Gaster’s explanation, his anger at his boss’s recklessness fizzled out. However, he didn’t want to see the man he looked up to turn to dust because of his strange self-sacrificing impulses. He needed to do something.

He straightened his lab coat, looked Gaster right in the eye sockets, and said, “please sir, let me assist you with your experiments.” 

Gaster blinked. This caught him off guard. He had not anticipated Sans to offer himself up to become his own personal test subject. He chuckled and said, “You only have 1hp. Why would I risk your fragile life if I’m unwilling to risk the lives of healthy monsters I don’t even know?”

“look doc, i just want to help you any way i can. don’t view me as just another monster you have to protect. instead, i ask that you view me as an extension of yourself. i… i want to be a tool or resource you can rely on in your efforts to help monsterkind. i truly believe that if the underground were to lose you, our hope for freedom will be lost.” 

Sans walked over, held out his hand and said, “so please sir, let me help you.”

At first, Gaster was speechless. In the five months he has gotten to know Sans, never before had he heard the typically lazy monster speak with such passion. 

The smirk he had earlier returned and his eyes dilated slightly. Sans was essentially submitting himself to him and that wasn’t an opportunity he was going to waste. He stood up out of his chair and enveloped the small skeletal hand with his own. He smiled a bit wider and said, “Sans, I would be honored if you were to join me on my mission to provide new and innovative ways to increase monsterkind’s standard of living while contained in our underground exile.” 

“and maybe one day we will find a way to free ourselves from this place, right doc?” Sans added. He had a smile on his face as he shook Gaster’s hand. A real smile, which was far different from the permanently fixed one he always had on his face. 

Just as Sans was about to pull away from their handshake, Gaster gripped the small hand a bit tighter and jerked Sans towards himself. 

The small skeleton let out a gasp of surprise as he was pulled roughly against Gaster’s chest. Gaster smiled with amusement as Sans glanced up at him in confusion. He was rather pleased to see a large blue blush spread rapidly across his assistant’s face. Casually, he reached down with the hand that wasn’t holding onto Sans and snatched his glasses out of the front of Sans’ lab coat pocket.

Releasing Sans’ hand he took a step back and let out a small chuckle. “Thank you, Sans, for keeping these safe for me. And don’t worry, I’m sure I can find _something_ interesting you can help me test very soon.” With that, he turned and walked out the door leaving behind a very flustered skeleton. 

The moment the door closed Sans let out a huge groan. He couldn’t believe how stupid he had made himself look in front of Gaster. The man had just pulled him close so he could grab his glasses and yet that was enough to get him to start blushing like a damn school girl. He could still feel the heat on his face, but perhaps that had more to do with the incredible amount of embarrassment he currently felt. 

Sans sat at his desk and rubbed at his flushed face. Soon the other members of the science team would start to trickle in and he really didn’t want them asking about his stupid face.

His coffee was cold now, but he didn’t really need to drink it anymore. He still felt a bit jittery after this morning’s events. The jitteriness eventually turned to apprehension as the day went on. His thoughts were constantly lingering on all the possible experiments his boss might have him be a part of. Dr. Gaster knew he only had 1hp so he seriously doubted it would be anything that would put his life in danger, but he could imagine there were still plenty of safe experiments that could be rather unpleasant. 

Perhaps he had acted a bit rashly when he made the decision to volunteer himself to the Royal Scientist.

Welp, nothing to do now but wait and see what the doctor had in store for him. Besides, he could always back out if he ever felt uncomfortable with an experiment, right?


	2. A Slight Mix Up

Sans was sitting at his desk trying to read a particularly dry science journal but his thoughts kept straying to other topics. After he caught himself reading the same line over again for the sixth time that afternoon, he gave up and ripped his red reading glasses from his skull in frustration. Sans leaned back in his chair and stared at the ceiling deep in thought.

It has been three weeks and Dr. Gaster hadn’t mentioned a single word about the personal experiments since the morning he had found the man stuck to the ceiling. Sans was beginning to think the doctor was going to carry on his self-experimentation despite their agreement to do it together. 

Part of Sans felt relieved because he didn’t want to be subjected to anything too risky, but the other part of him really wanted Gaster to trust him enough to include him in his personal experiments. Why was he so conflicted about this?

Sans could feel his eyes start to droop and it wasn’t long before he was snoozing peacefully in his chair. 

-BAM!-

Sans yelped and jerked awake. 

Much to his dismay, a very displeased looking Gaster was standing in front of him with his right hand firmly planted on his desk. 

“Sans, this is the fifth time this month I have caught you sleeping at your desk. That means it is highly probable that you have slept at your desk for periods of time in which I have not caught you. Correct?”

Sans gulped. Gaster was right. He usually took a nap nearly every day during work, but he was typically careful enough not to get caught. He was off his game this month.

“i’m really sorry sir, but i can’t always help it. my doctors believe it has something to do with my 1hp. apparently my soul has trouble regulating my hp, and it’s constantly sapping my energy trying to give me more hp without actually giving me anything.” Sans hated talking about his weakness but he felt Gaster deserved to know the truth. 

Gaster’s expression changed from anger to concern in a flash. 

“My god Sans, why haven’t you told me about this? There is a lot of heavy machinery around here. What if you fell asleep while operating one of the more dangerous machines?”

“nah doc, it doesn’t work like that. i only start to fall asleep if i get too comfortable. as long as i stay alert i’m fine.”

The royal scientist didn’t look convinced. “Are you on any medication?” he asked.

Sans sighed and rubbed his skull. “i’ve tried multiple medications but i haven’t found anything that has helped yet.” 

Gaster was in deep thought for a few moments before he smiled and said, “Sans, I believe I have something that could possibly help you.” 

Sans’ eye sockets widened with surprise, “r-really, doc?” 

“Yes! But it’s untested and would require some fine tuning. Why not stop by my personal lab after everyone leaves and we can run some tests?” 

Sans didn’t hesitate for a second, “yeah sure, that sound great!” He has been burdened by this condition his whole life and the thought of being rid of it made him very eager indeed to see what Gaster has planned. 

“After the tests I’d like to show you this new concoction I’ve been working on. It can grow hair on any surface with a single drop!” Dr. Gaster smiled and clapped his hands gleefully. 

Sans opened his mouth to question Gaster about why he felt the need to create such a thing, but instead, he shook his head, grinned and said, “that seems very interesting, sir.”

Dr. Gaster was definitely an odd bird. 

That night after everyone left, Sans entered Gaster’s personal lab. He honestly wasn’t nervous at all about the experiment until he saw Gaster standing next to an examination table. The sight of the table caused Sans’ soul to pulse like an actual heartbeat. 

“Ah, Sans, I’m glad you came. Just take off your shirt and hop up onto the table so we can get started.” 

“m-my shirt?”

“Yes, I require access to your soul which we both know is housed within your ribcage. You can keep your lab coat on if that makes you feel better. I just need your ribcage to be visible.” 

Sans slowly nodded and pulled off his tie before fumbling with the buttons of his shirt. This would be a lot easier if Gaster wasn’t staring at him. 

Once he dropped his shirt to the floor he reapplied his lab coat and hauled himself onto the table. At least this type of table had back support so he wasn’t going to be lying flat on his back the whole time.

“Very good. Let us begin shall we?”

Gaster opened up a cabinet and pulled out a flask. He walked back to Sans and handed it to the small skeleton.

“Let me explain how this drug is going to work. First, it will put you to sleep, and then as you sleep it should begin to suppress your faulty health regeneration process. This should give you a full night’s sleep without wasting the energy the faulty regen processes was using up. Furthermore, the suppressor should last about 24 hours, so should this work, you will be required to take it every night before you go to bed. It is my hope that with this drug you should have no more problems staying awake during the day.”

Sans grinned at that and took the flask from Gaster. 

“Drink all of it. I’m only giving you enough to put you out for a few hours so that I can make sure everything is working correctly.”

Sans looked down at the flask. The liquid was a thick blue substance with small flecks of yellow in it. Sans did as he was told, and with only slight hesitation he downed the contents.

Sans immediately gagged. It tasted awful. Like liquid crayons. He didn’t know how he managed to do it, but he drank the whole thing without spilling a drop. 

Gaster took the flask from him when he finished. He then reached above Sans to lower the armrests… armrests that had leather straps attached to them.

Every bone in Sans’ body stiffened at the sight of the straps.

“wh-wha-“

“Please place your hands through the straps, Sans. I believe there is the potential risk of sleepwalking with this concoction and I don’t want you to accidently fall off the table.”

Gaster gave Sans a reassuring smile.

Sans’ hands were shaking slightly as he slid them through the straps. Gaster tightened each strap before latching them securely. His shaking hands apparently did not go unnoticed because as Gaster secured the last strap he gently squeezed one of his shaking hands and whispered, “Don’t worry.”

Sans looked up at Gaster. “i’m not afraid,” he lied. 

Gaster straightened up and said, “Excellent because the next part is a little tricky.” He held up a cord that was attached to a monitor.

“I need to attach this sensor to your soul. We only have about 15 minutes until the drug starts working and in that time I’d like to get a base reading of your soul.” 

The soul was such an intimate and delicate object. Sans’ soul was particularly fragile due to his 1hp. He didn’t let just anybody handle his soul, and he was already feeling unsafe because of the straps holding down his wrists. 

“i don’t know about this, doc.”

“Nonsense, I’ll be gentle.” 

Sans didn’t particularly like the way Gaster was smirking at him. Actually, it was kind of creeping him out.

“w-wait!”

But Gaster had already started to push his hand up into his ribcage. 

“I’m sorry Sans, but time is of the essence and I need these readings so I can make sure your soul remains stable during the experiment.”

The instant Gaster touched his soul, Sans gasped and shivered. The soul was an erogenous zone for monsters, and right now small bolts of pleasure were ripping through Sans’ whole body. He was trying very hard to keep his composure as Gaster clasped the sensor to his oversensitive soul, but it was getting increasingly difficult. 

Gaster watched his assistant’s facial expressions with fascination as he worked to attach the sensor to the small skeleton’s soul. Sans had his eye sockets shut tight and his teeth were clenched even tighter, but no matter how much Sans tensed up he couldn’t hide the small shivers that passed through him.

For a brief moment Gaster’s right eye flashed purple. 

Don’t lose control.

As soon as he had the sensor attached, Gaster removed his hand quickly from Sans’ soul. He needed to stay in control. He didn’t want to hurt Sans by mistake. Looking down at his hand he noticed traces of Sans’ blue soul essence. He nonchalantly wiped the sticky blue substance onto his black lab coat. He didn’t care if his coat got dirty, that’s what it was there for after all.

The moment Sans felt Gaster’s hands leave him he opened his eyes and glared at the royal scientist. 

“i suggest next time you allow me to consent before you decide to fondle my soul, _sir_.” 

Gaster looked genuinely hurt by the comment. “Sans, I’m so sorry. You’re right, sometimes I get a bit too eager and I forget myself. I promise from this point on I’ll explain my intentions better, but please understand that I really do have your best interest in mind.” 

Sans exhaled a breath he didn’t even realize he had been holding and looked away from his boss. 

“look doc, I know you mean well, but just be careful alright?” 

The scientist nodded and said, “I’ll be careful Sans, you can trust me.” 

Sans looked back up at the royal scientist and gave him a small smile. “I do trust you, sir.” 

Gaster returned the smile and clapped his hands together. “Well, the hard part is over. Now I’m going to record your soul readings. You should start to feel the effects soon so just tell me when you notice any changes.”

The first 10 minutes were completely uneventful. Sans just watched quietly as Gaster wrote down his soul readings onto a clipboard. 

Then he started to feel a bit funny.

Was it getting hot in here?

Sans squirmed in discomfort. Why was it so damn hot? Was core malfunctioning? He suddenly wished he hadn’t kept his lab coat on.

A minute later could feel himself beginning to sweat. He looked at Gaster for any signs that the man was feeling the same thing as him but the other skeleton appeared completely unaffected by the temperature change. 

“hey doc?”

“Hum?” the scientist didn’t take his eyes off his clipboard as he acknowledged Sans. 

“do you feel warm at all?”

Gaster looked up. “No why?”

“it feels like i’m getting cremated over here!” Sans joked and laughed nervously. 

Gaster furrowed his brow as he watched a bead of sweat drip from his assistant’s skull. Hot? That was definitely not something Sans should be feeling. He tapped his pen to his mouth in thought. 

His eye sockets widened as realization hit him like a ton of Temmies. He shot up out of his seat, his clipboard and pen clattered to the floor. He ran over to the cabinet that he had pulled the flask from and began rummaging frantically through it. 

When he reemerged he was holding a flask that looked almost identical to the one Sans had taken. 

Gaster looked from the flask he was holding to Sans. “Uh-oh,” he deadpanned. 

Sans went ballistic. “uh-oh. _uh-oh?_ what do you _mean_ uh-oh? what the hell did you do to me, _wingdings_!?”

Gaster’s hands rose up in defense. “I might have accidentally given you a different experimental drug I had been working on. Have no fear, for I’m quite sure it’s harmless!” Gaster attempted to give Sans reassuring smile but it came out nervous looking and not reassuring at all.

“just tell me what it does,” Sans bit out as calmly as he could. He wanted to be angry at Gaster, but the heat was already unbearable without him getting all worked up. 

“It’s a drug that forces a skeleton to go into heat. Have… have you ever been in heat before, Sans?” Gaster asked carefully. The topic of going into heat was not something skeletons typically discussed with their boss. It’s an embarrassing period of time when a skeleton’s body cries out for a mate. Skeletons also often experience a significant loss of self-control during this time. 

Sans blushed and whispered, “yes.” 

He had gone into heat before and it was not a fun experience. Besides getting really warm, he became incredibly aroused and extremely hostile. Before he realized what was happening he had almost attacked his own brother! Poor Papyrus was so confused when Sans knocked him to the ground. Thankfully Sans managed to shove himself away from his bro, and flee into his room where he stayed isolated for a whole week. 

“why the hell would you create a drug like this doc?” Sans groaned. 

The expression on Gaster’s face changed from concerned to something much colder almost instantaneously. 

The lights in his eye sockets turned purple and in a hushed voice he said, “Because I can.”

**Notes for the Chapter:**

> Uh-oh.


	3. Control

Sans looked into Gaster’s glowing purple eyes and immediately felt dread. “what did you just say?”

Something was wrong he could feel it. Sans tried pulling at his bindings in an attempt to free himself but it was useless. He wasn’t going anywhere.

“You heard me, Sans. I create these experiments and experiment on myself simply because I can. I don’t do it out of any sort desire for good or evil. I do it because I can, and therefore, I believe I have too.” Gaster shrugged and his purple eyes flashed aggressively. 

The scientist took a step towards Sans but abruptly stopped. Pain flashed across the older skeleton’s face and he rubbed the crack above his right eye. 

Gaster then suddenly bent over and picked up the clipboard and pen off the floor. When he rose back up his eyes were back to normal. The expression on his face wasn’t cold anymore. Gaster was looking at him as if nothing happened! What the hell?

Gaster saw the frightened look on Sans’ face and frowned. “Are you alright Sans? I’m sorry about the mix up. I’ve been a bit more distracted than usual lately.” Gaster rubbed the crack above his right eye again.

“uh… doc? Your eyes turned purple for a moment there.” 

The royal scientist smiled and said, “Well purple is the color of my magic Sans, I’m sure I’ve used it around you before.” Gaster emphasized his point by snapping his fingers and conjuring a set of purple floating hands. The hands took the clipboard and pen away from Gaster and began jotting notes down for him.

Gaster’s eyes were purple due to the magic required to maintain the floating hands, but they weren’t cold like the ones he had seen before. 

“heh, I guess that’s pretty _handy_ huh?” Sans joked weakly. “except, well… you were sayin’ some pretty weird stuff, doc.”

“Like what?” the older skeleton inquired.

Sans relayed everything Gaster had said to him during his weird… trance? When he was done Gaster looked uneasy. 

“That doesn’t sound like me at all Sans. Are you sure the heat didn’t cause you to misinterpret things?”

Gaster gently rested his hand on Sans’ forehead and the small skeleton couldn’t help but to lean into the touch and close his eyes. 

Maybe he had imagined the whole thing. His body felt like it was boiling. Perhaps he had a heat-induced hallucination or something. 

While Sans was questioning his hold on reality, funny enough, Gaster was doing much of the same.

Gaster couldn’t believe he had lost control like that. He knew he had lost control because of Sans’ innocent inquiry into his motives. Sans’ question should have been easy to deflect without losing control! He was sincerely regretting upping the dosage of his Determination tablets so soon. 

He had expected some mild loss of control, but nothing dangerous. He would have to reevaluate his options at a later time. If Sans wasn’t here, he would isolate himself and meditate to prevent further loss of control. Unfortunately, Sans was in a bad state right now and he couldn’t possibly abandon his assistant at the moment. He just had to remain focused and alert to prevent his Determination fueled alter ego from making another appearance tonight. He could do that. He knows that he is fully capable of maintaining control over this thing.

There was one more thing. He could have sworn he labeled his experimental substances correctly. He knew the Determination was causing him to be a little more reckless, it has been that way since the accident… since he had liquid Determination injected directly into his own skull, but he didn’t think he would become reckless enough to mislabel substances he intended on using on other monsters.

Gaster decided to file these thoughts away for further scrutiny later. Right now Sans needed him.

“Sans?”

The small skeleton opened his eyes and blushed furiously when he realized how heavily he was leaning into Gaster’s touch.

He pulled away slightly and said, “sir?”

“That flask you ingested contained three doses of the skeleton heat mixture. I know you said that you’ve experienced skeleton heat before but this one will be much more severe. I’ve never had a test subject ingest that much before so I don’t know how this will affect you, but if you need anything at all I’m here for you alright? You only need to ask.” 

Sans looked away from Gaster and mumbled something the royal scientist couldn’t quite make out. The blue blush Sans was currently sporting was starting to spread down his neck and onto his clavicle. 

“What was that?”

“i… i need you to t-touch me,” Sans whimpered. He was completely mortified. Did he really just ask his boss to touch him? He was so fucking fired.

Gaster’s voice broke through Sans’ internal tirade. “Where do you need me to touch you, Sans?” 

It was Gaster’s turn to get a little flustered. A light purple blush dusted the tall skeleton’s facial bones. He has known for a few months now that Sans held some kind of affection for him, and he had to admit he greatly enjoyed making Sans blush while they worked together in the lab, but there was a big difference between flirting and… this. 

Sans groaned as his arousal spiked. He wasn’t expecting Gaster to respond so positively.

“please,” Sans panted, “i need… ugh. just touch my neck please.” 

“Like this?” Gaster grasped Sans’ neck gently and stroked down slowly. He made sure to press his thumb a little harder between the indents of Sans’ cervical vertebrae.  
Sans spasmed and gasped at the intense sensation of Gaster’s hand massaging his neck. 

Gaster knew he shouldn’t be enjoying this. Sans was basically drugged out of his skull and bound to an examination table, which sounded _really_ bad now that he thought about it, but he couldn’t help himself. Sans was just so goddamn responsive to his touch. 

“mmm… g-gast-er, i need more,” Sans mumbled. 

The royal scientist used his other hand to grab onto Sans’ clavicle. He began to gently rub the bone in small circular motions. This placated Sans for about all of 5 minutes. 

“ugh. not enough!” Sans looked up at Gaster and the scientist could see aggression on the younger skeleton’s face. “untie my wrists so i can help you.”

Gaster withdrew both his hands and Sans whimpered at the loss of contact. He took off his glasses and cleaned them with his coat before placing them back onto his face.

“I’m sorry my dear assistant, but you know as well as I do that the moment I release your restraints you’re most likely going to assault me in your aggravated state. We don’t want that now do we?” 

Gaster looked over at the floating purple hands to make sure they were recording onto the clipboard when exactly the aggressive behavior began. This was still an experiment after all. Even if it wasn’t the one he intended to conduct today. 

Sans growled with agitation at the lack of contact. “can you do something please? anything!?” 

Gaster frowned when he realized he couldn’t do much from this vantage point. After a moment of thought, he concluded he needed a better angle if he was going to continue. Without any hesitation, he pulled himself onto the table and straddled Sans’ lap. 

Sans couldn’t hold back his moan at the sudden contact. “Ah! shhhiit!”

He was thrilled by Gaster’s boldness and the aggression he felt earlier ebbed away. Gaster made sure to make note of that of course.

They stared at each other and for a moment, neither of them knew what to do. Honestly, Sans couldn’t believe this was happening and his mind just sort of went blank. Eventually, Gaster slowly brought his hand up to Sans’ chin and lazily scraped his thumb against the smaller skeletons mandible. Sans shuddered and he could feel his eyes dilating but he managed to maintain eye contact with the older skeleton. 

“You’re rather aesthetically pleasing to me Sans,” Gaster purred. “I particularly enjoy watching you react to my touch.” Gaster grabbed Sans’ ribs roughly with both hands and the small skeleton underneath him moaned and arched his back. He absolutely loved the sounds Sans was making and he wanted more, but In the back of his mind, a small voice reminded him not to lose control. 

When Sans’ mind pulled itself back together he stammered, “c-can we… i mean. it’s stupid, but can we… um.” 

Gaster waited patiently for Sans to gather his thoughts. While he waited he played with Sans’ ribs. Taking time to lightly massage each rib individually. 

Sans finally blurted out, “can you kiss me please?" Sans immediately began berating himself for his total lack of finesse. Oh my god. Did he just ruin the moment by acting too needy?” 

Gaster paused his caressing. 

A kiss? He didn’t know why the thought of kissing gave him pause as he has already done so much worse to Sans tonight and planned to do so much more. He quickly realized it was the symbolism behind the act that worried him. 

Sure, he and Sans were already engaging in acts that would be considered very intimate, but he could always pass those acts off as just his way of helping Sans through his heat. A kiss was a declaration of desired companionship between two individuals and… uh… hmm, perhaps he was too old-fashioned… You know what? Fuck it!

-Clack!-

The royal scientist pressed his teeth hard against his assistant’s teeth.

**Notes for the Chapter:**

> Just throw me into a trashcan and launch me into the sun.
> 
> Also only Gaster can get away with saying something as dumb as "You’re rather aesthetically pleasing to me."


	4. Tongue-tied and Determined

In all honesty, skeleton kisses weren’t very gentle. There wasn’t any flesh to prevent teeth and bone from clashing and grinding painfully together. It might have been rough, but to Sans, it felt amazing. There was just one problem.

This heat was driving him flippin’ crazy! 

He desperately wanted to bring himself closer to the man above him and deepen the kiss, but these stupid straps around his wrists prevented him from being able to wrap his arms around the taller skeleton. 

As he sulked, a devious idea seeped into his mind. He had a certain trick he had been dying to try and well… he figured that this was the perfect opportunity to finally try it out.

As Gaster pressed his teeth against Sans’, he began to wonder why he had hesitated at all, this was excellent! He had always thought kissing was pointless for skeletons considering they weren’t equipped with the necessary physical features to properly engage in the task, but now he could see he was wrong. This ‘kiss’ was triggering all the right endorphins making for a rather pleasurable experience! He began to wonder if he cou-

Gaster’s entire thought process was cut off by the feeling of something warm and wet prodding against his teeth. Confused, he pulled back.

Below him, Sans had his right eye socket closed but his left eye socket was open and glowing with his signature blue aura. Between the small skeleton’s teeth was… a blue tongue? How fascinating!

Before Sans could retract the tongue back into his mouth, Gaster’s hand shot up and grasped it hard. Sans let out a small cry of surprise and tried pulling away but Gaster held the tongue firmly between his thumb and forefinger. 

“Sans… did you use your magic to create this?” the scientist asked. 

Gaster’s face betrayed no emotion but his tone was severe. Did he do something wrong? Sans could only nod his head a little and cringe. He really wished Gaster would let go. His grip on his tongue kind of hurts!

Gaster noticed Sans’ discomfort and brought up his other hand to lightly touch the summoned appendage with his pointer finger.

“Interesting, you also appear to have feeling in this magic muscle.” Gaster was talking more so to himself than to Sans at this point.

After a few more pokes and prods Gaster released his tongue. The scientist then smiled brightly at him and said, “This is brilliant Sans! I’m sure I can find many interesting applications for something like this.” 

Gaster had never thought to create a tongue out of magic before. Skeletons didn’t need tongues to talk or eat, but he was sure he could make use of this ability somehow. He made a mental note reminding him to ask Sans later about how he came up with the idea. 

“Hum… I believe I would like to give it a try and there’s no time like the present, correct?” The purple aura in Gaster’s eye sockets flared as he gathered his magic.

Sans watched with rapt attention as Gaster opened his mouth and felt a shiver run up his spine when a long and purple tongue unfurled from between the tall skeleton’s teeth. 

“Does this look satisfactory to you Sans?” The scientist asked with uncertainty.

“uhhh….”

Holy shit. 

Sans couldn’t take it. He needed Gaster. He needed Gaster right now!

The scientist smirked at the hungry, longing look currently displayed on his young assistant’s face. Without further ado, he grabbed Sans’ clavicle and pulled him towards himself, causing Sans to inhale sharply. He then placed his other hand on the back of Sans’ skull to hold him still as he plunged his newly acquired organ into the surprised skeleton’s mouth.

The two tongues met and briefly battled for control, but Gaster’s easily dominated. Sans relinquished control with a soft moan. 

Free to do as he pleased, Gaster began exploring the confines of Sans’ mouth. He ran his tongue over Sans’ teeth finding them to be relatively flat, save for several exceptionally sharp canines, which he flicked his tongue at playfully. At one point during his exploration, he accidentally pushed his tongue a tad too far and gagged poor Sans in the process. 

He pulled away momentarily to whisper apologies and then quickly transitioned to lapping at the roof of Sans’ mouth, causing Sans to let out a few low murmurs and whimpers.  
He eventually brought his tongue back to Sans’ and the two agile muscles engaged in a wonderfully erotic dance: Twisting, twirling, touching, it was all so warm, so wet, so _right_. He wanted more. He needed more.

The purple lights in Gaster’s eye sockets began to flash aggressively, periodically switching from a warm/light purple that corresponded with his magic, to a dark/cold purple that was completely foreign to the scientist’s magical signature. Sans took no notice of this as he currently has his own eye sockets closed in pleasure. 

Being the impatient man that he was, Gaster released the hold that he had on Sans’ clavicle and slowly lowered his hand until it was brushing against the spine just below Sans’ ribcage. 

Without any warning, he grasped the vertebrae and quickly stroked down hard and fast.

Startled, Sans Jolted and let out a muffled cry.

“mumphh!” 

Gaster extracted his tongue from Sans’ mouth and said, “Don’t talk with your mouth full Sans, it’s rude.” He couldn’t contain a smug smile from spreading across his face.  
Sans shot the snarky scientist what he had hoped was an intimidating glare, but Gaster just laughed and stroked his spine again.

“fuck!” 

Sans swore again and threw his head back, moaning as powerful waves of ecstasy crashed through his body. Not giving him any time to recover, Gaster ran his hand down Sans’ spine again. Sans cried out and rolled his hips, bucking himself against the older skeleton’s pelvis. A hot bolt of pleasure shot through the scientist taking him by surprise. 

“Oh! Mmmh…” Gaster had to bite down on his knuckle to prevent himself from crying out. When the pleasant tingling sensation subsided, he looked down at Sans and froze. Sans looked… _absolutely wonderful_. The lights in Sans’ eye sockets appeared hazy with lust and need, his cheekbones were completely flushed blue, and he had saliva starting to drip from the corners of his mouth. His assistant looked so desperate, so _vulnerable_. 

It was at that exact moment Gaster’s highly valued control completely disintegrated to dust. Funny… it vanished so fast it’s almost like there never really was any control to begin with. 

Sans squirmed when Gaster ceased touching him. “why did you stop? please… i need more.” Sans whimpered between pants.

When he got no reply he sat up a little straighter to get a better look at the immobilized skeleton above him.

Gaster’s face appeared to be entirely devoid of emotion. His eyes, however, were leering right at him with a mixture of cold resignation and predatory hunger. Sans’ eye sockets widened as an upsurge of fear washed over him.

Dammit! He knew there had been something wrong with Gaster. Heat-induced hallucinations my tailbone! 

“d-doc?”

Gaster reached up and stroked Sans’ cheek. “Why do you look so afraid, Sans?” Gaster’s tone sounded sweet and caring but the expression on his face remained completely unchanged. 

Sans swallowed and took a deep breath. It was hard to maintain a proper thought process through the heat but there was dire question boiling inside of him at a temperature that was far greater than the heat he currently felt. 

“who are you?” Sans demanded.

Gaster’s hand immediately stilled. “What do you mean?”

“cut the crap. i know gaster, and you’re definitely not him.” Sans couldn’t exactly pinpoint what it was that made him believe this wasn’t his gaster. He just had a really bad feeling.

“Oh Sansy, I _am_ Gaster. I’m just a little more _determined_ than usual that’s all.” 

“what is that supposed to mean?” Sans spat. “what are you so determined about?”

Gaster laughed and said, “I’m determined about many things my dear assistant,” Gaster growled, “but right now I’m very determined to get you to cum for me.” 

“wha- AHHH!” 

Sans screamed as Gaster ran his tongue along his spine, pausing periodically only to kiss and bite at each individual vertebra. Sans turned into a writhing, blubbering mess. It all felt so bad and so good at the same time. 

Gaster leaned up and began biting and licking Sans’ neck, effectively distracting the small skeleton while he snapped his fingers and summoned two dark purple hands to make quick work of Sans’ khaki work pants. When they were out of the way Gaster stopped what he was doing to admire his assistant’s naked body beneath him. “Beautiful. Just look at how much you’re body needs me.” Gaster held his hand out a few inches above Sans pelvis and Sans couldn’t help but to arch himself towards the older skeleton’s hand in desperate need for friction. 

Gaster just laughed and held his hand up higher, preventing Sans from achieving his goal. Sans whipped his head up and snarled, “fucking touch me now or i’ll tell everyone you sleep with your thumb in your mouth!” It was a pretty lame threat, but it was all the leverage Sans had right now.

Gaster laughed again and said, “You are in no position to be making threats my dearest little assistant, but if you want to play the blackmailing game I can accommodate you.”  
The slightly deranged scientist summoned another pair of hands that dug through one of the cabinets and reemerged holding some kind of device.

“wh-what the hell is that?” Sans asked. 

Sans knew perfectly well what it was he was just sincerely hoping he was wrong.

“Why, it’s a video camera!” Gaster said with enthusiasm, which was really weird because his face was still bereft of emotion. “I use this video camera to record some of my experiments, and this is an experiment is it not?” The floating purple hands removed the lens cap and flicked on the power button. Sans watched with mortification as a little red light blinked on indicating that the camera was now recording. 

Gaster tilted Sans’ chin so he was looking directly into the glass lens. “Say hello to the camera Sans!”

**Notes for the Chapter:**

> Sorry it took so long to get this out, I was really sick for a while. 
> 
> Feel free to leave a comment! I love reading comments even long after my stories have been posted. Just wanted to let you know I appreciate you guys! :D


	5. Something Is Seriously Wrong with Gaster

No way. This couldn’t be happening!

Gaster released Sans’ chin. “Now, I’d really like to see if I can release you from this heat without even having to touch your soul. I think that would be a very interesting experiment. Something worthy of filming” He gently ran his fingers along the ridges of Sans’ pelvis, silently contemplating his next action.

Sans chuckled darkly. “heh, aw jeez boss, you’re not even gonna buy me dinner first?” The question was dripping with sarcasm but it caused Gaster to still his movements and look up. The older skeleton blinked and the lights in his eye sockets dimmed ever so slightly. “Would… would you like to have dinner with me later Sans?” 

Of all the things Sans was expecting Gaster to say, that had definitely not been on the list. 

“what!?” Sans hissed. “ _now_ you want to ask me on a date after everything that’s happened tonight?” Sans was pissed. Gaster must be freaking coo coo for MTT-Brand Cocoa Puffs if he thinks he can just ask him out like this. He was naked and bound to the examining table for God’s sake! 

Okay, sure, he would have probably said yes if Gaster had asked him out not even three hours ago before all this crap happened but now…? Sans stopped that train of thought because he was starting to upset himself.

For the first time since Gaster’s change in behavior, Sans noticed genuine emotion passing over the older skeleton’s face. He looked pained and confused. The scientist then clenched his eye sockets shut tight and brought his hand up to his skull and started rubbing at the crack above his right eye socket compulsively. 

After a few moments Gaster stopped rubbing his skull but still appeared to be in some kind of physical pain when he growled through gritted teeth, “No, you’re completely right. I have no idea why I asked such an idiotic question.”

Before Sans could do or say anything, Gaster pressed another kiss to his mouth. The kiss they had shared before Gaster started acting strangely was perhaps not exactly gentle, but it was playful, curious, and even a bit clumsy. This kiss was entirely different. This kiss was direct, demanding, and gave the impression that Gaster knew what he wanted and he was going to take it without hesitation. 

This wasn’t right. Something was seriously wrong with Gaster, and yet Sans couldn’t help but melt into the kiss. He was having a hard time getting his body to obey his mind when his body was so hot and tingly. 

Sans groaned but stopped abruptly when he heard his own groan echoing from the camera hovering nearby. That’s when it dawned on him how truly naked he was. He was naked and Gaster was fully clothed, and clearly not quite in his right mind, on top of him. He had never felt more exposed in his life and the camera was definitely not helping. It felt like an extra set of judging eyes, only these eyes were recording every sound and every movement he made. 

Sans felt humiliated and his face burned in embarrassment. Everything from his clothes to his dignity had been stripped away without him even realizing it by a man he trusted and now a camera was documenting this shameful display. Sans could feel his soul throb as panic filled him and he thrashed against his restraints. He didn’t like this. He didn’t like this at all!

Gaster gripped the small panicked skeleton by the shoulders and shot him a questioning look. Sans stopped struggling and looked up at the man with pleading eyes and begged, “please, i don’t like this. turn it off.” Sans nodded towards the camera.

Gaster placed a long, elegant finger against Sans’ mouth and said, “Shhh… I wouldn’t worry about the camera Sans. As long as you behave you have nothing to fear.” Gaster then lowered himself until his mouth was lightly pressed against the side of Sans’ skull and he whispered, “But if you don’t, I’ll make sure that sweet, innocent brother you’ve told me so much about receives a copy of this video. I wonder what he would think of his big brother after seeing just how lewd you really are.”

Papyrus!? Sans stiffened and began to feel a little faint. The pupils in his eye sockets vanished and he was struggling to breathe. N-no no! He couldn’t let his bro see him like this. How would he even begin to explain to Papyrus about what Gaster was doing to him? How was he supposed to explain to his pure hearted little brother that he was drugged and sexually assaulted by his boss who went totally insane? 

No way… there was just no way he could deal with that.

Even with the heat, Sans managed to break out into a cold sweat. Feeling disgusted with himself, Sans hung his head and muttered, “no please, i’ll behave.” As soon as the words left his mouth Sans cringed at how pathetic he sounded.

Gaster, however, seemed delighted. His eyes lit up and he clapped his hands together. “Excellent! I knew you’d see things my way.” Sans sent him a nasty scowl. Well, as nasty of scowl he could manage with this fixed grin on his face. He just didn’t understand. He didn’t understand why Gaster was so cruel all of a sudden, and Sans wasn’t buying the whole, ‘I’m just a little more determined than usual’ excuse. No, there was something more to this.

One thing Sans noticed was that there had been an actual physical change in Gaster’s magic around the time the scientist started behaving differently. The first pair of magic hands Gaster had summoned were still floating around holding the clipboard and they were a much lighter purple than the hands holding the video camera. Magical signatures don’t just change like that. 

If Sans had to guess, he was witnessing the product of a failed experiment. It made sense didn’t it? It was practically Gaster’s MO to test dangerous experiments on himself because he was a self-destructive idiot! 

“Just sit back and relax Sans, I promise that all I want is for you to feel good. I want to rid you of this skeleton heat by bringing you to release. So please, don’t fight me.” Even though Gaster’s facial expression was completely deprived of emotion, his eyes were like smoldering purple flames. Sans swallowed thickly as Gaster continued to run his hand along the ridges of his pelvis. 

Gaster raked his eyes over Sans’ naked body. “Hum… but what am I going to do with you?” The small skeleton shivered involuntarily. 

“doc, can i ask you a question?”

Gaster snapped out of his musings and said, “Of course Sans! What do you want to know?” Sans flinched at Gaster’s cheerful demeanor and he took a deep breath to ease his nerves.

“look, i think we can both agree that you are not your usual self right now, right?” Gaster didn’t say anything so Sans continued, “you told me i could help you with your personal experiments remember? so i gotta know doc, what’s causing you to act so out of character?” ‘out of character’ was putting it lightly but he didn’t want to offend Gaster.

“What makes you think I’m acting out of character?” Gaster asked coolly as he lightly caressed the smaller skeleton’s neck. His purple eyes were fixated on Sans’, and Sans felt extremely unnerved by their piercing stare.

Sans turned away so he couldn’t see those awful eyes. “be-because… because you would never do this! you’re not a cruel person, and you would never force me to do things i didn’t want to do!” Sans could feel tears threating to spill over but he refused to let them fall. “please, i don’t like you like this, gaster! i want my old boss back, the smart and reckless idiot that i care deeply for. i know you’re in there somewhere doc, i know you can fight this!” Sans was practically shouting at this point. His soul throbbed with pain.

“I’m sorry Sans.” 

Sans looked up to see Gaster looking at him with a deep sadness in his eyes. 

“I’m sorry… but you don’t seem to know me as well as you think you do.” The sadness was gone instantly and in its place was what can only be described as total apathy.  
Sans gasped as the hand on his neck wrapped around his throat tightly. Not tightly enough to completely cut off his air, but enough to keep him from being able to move. 

“please stooop!” Sans cried.

“I can’t.” 

“why?” Sans croaked. A tear rolled down his cheek. 

Gaster gave a small shrug of indifference. “Like I told you before, I do what I do simply because I can. There is no right or wrong, moral or immoral. If I’m determined enough to do something I will do it and nothing is going to stop me.” He used his unoccupied hand to undo the buttons at the front of his dark gray slacks. Sans’ eye sockets widened and he tried to shake his head but he couldn’t move. “no no, please no!” 

Gaster tightened his grip on Sans’ throat. “Be silent,” he snarled. Sans clung the padded armrests so tightly he was sure to leave permanent indentations in the plush material.

The tall skeleton aligned the front of his bare pelvis with Sans’ and gave a small testing thrust. Sans’ breath hitched and Gaster let out a hiss of satisfaction. He thrust again, harder this time and Sans couldn’t prevent the moan that escaped from his mouth as pleasure crashed through his system. “Oh Sansy, you feel so good,” Gaster whispered as he continued to rock his pelvis against his needy little assistant’s. 

The tears dissipated and Sans flung his head back and groaned. Maybe it was just the drug making him feel this way, but holy hell did this feel good. 

Gaster lowered his hand from Sans’ throat and grabbed his shoulder instead. His other hand was holding onto Sans’ leg, lifting it so that he could achieve a better angle. Gaster ground down hard onto Sans’ pelvis causing the smaller skeleton to cry out, “oh! ahahhh… g-gaster! i..i need- mmm!” Gaster slowed his thrusts. “What do you need Sans?” Sans glared at the skeleton above him before looking away in shame. “i… i need you to move faster,” he mumbled.

Sans’ heat has reached its peak. As much as he tried to deny it, he was addicted to Gaster’s touch. Addicted to the way the man moved against him. There might have even been a small sick part of him that enjoyed how rough Gaster was handling him. He would never ever admit that of course. 

Gaster chuckled, “What’s that? You want me to move slower?” The scientist brought his movements to a crawl. “wh-what!? no! i said move faster!” Sans arched himself trying to procure what he desired. “Oh! you wanted me to go faster? Why didn’t you say so?” Gaster came to a complete stop. Sans looked up at Gaster with utter disbelief. The lights in Gaster’s eye sockets gleamed with mischief. “What? I didn’t hear you say _please_.” 

Sans gaped at the older skeleton. How could this man be so cruel one minute and act like a child the next? He shook his head. As troubling as his bizarre mood swings were, at least he wasn’t looking at him with such cold indifference anymore. 

“for the love of god doc, please _please_ move faster!” 

Gaster let out a bark of laughter and then growled deeply, “Okay, but try to remember that you asked for it.” He didn’t give Sans anytime to brace himself as he grabbed onto Sans’ pelvis with both hands and began thrusting rapidly against the smaller skeleton. Sans yelped at the sudden stimulation and stammered, “h-hoollyy sh-shhitt!” Sans’ speech became more and more disjointed with each thrust. 

He could feel his soul starting to rise out of ribcage. 

“mmm... g-gaster! so good, i’m s-so close!” Sans panted. He was drooling rather heavily now, but with his arms tied up, he couldn’t wipe it away. 

“Then cum for me my dearest little assistant,” Gaster cooed. The older skeleton could feel his own soul trying to rise out of his chest but he wouldn’t allow it. This had never been about _his_ pleasure after all. Gaster deepened his movements.

“help!” Sans suddenly cried, “I c-can’t! you gotta take the sensor off my soul please!” he whined. The sensor was too tight on his soul! He needed it gone or he wouldn’t be able to… he wouldn’t be able to find release! Shit! 

Gaster had completely forgotten about the sensor tethered around Sans’ soul. He reached up and ripped the sensor off, tossing it to the floor. He then gently grabbed the dripping soul and brought it to his mouth where he let his tongue run over it. 

Sans couldn’t handle it. The feeling of Gaster thrusting against him while his warm wet tongue lapped at his soul pushed him over the edge. He stiffened and cried out as his soul quivered and spewed blue soul essence all over Gaster’s hand. 

Sans saw stars as his orgasm slammed through him. As it faded so too did his vision. Darkness crept in slowly and the last thing he saw before the darkness consumed him was Gaster’s shell-shocked expression. His pupils were back to their normal white glow.

**Notes for the Chapter:**

> Hnnnghhhhh... It took me forever to write this one because I was so indecisive. I think i rewrote this chapter like 7 times. There was even a version of this chapter where Gaster beats the shit out of Sans and carves his initials into his pelvis with a scalpel. But I was like wtf... I want gaster to be an asshole, not a total psycho. This is why I can't have nice Undertale things because I brutalize it! every. damn. time. 
> 
> welp here you go! :D


	6. Gaster's Lament

Gaster blinked. He looked from his right hand holding the dripping blue soul to his unconscious lab assistant. He looked back and forth between the two, not quite understanding what he was looking at. Was this a dream? No, this was more akin to a nightmare. 

He gently placed the spent soul back into Sans’ ribcage where it belonged. He then slowly got off the examination table, being careful not to disturb the smaller skeleton, and walked over to the sink where he turned on the faucet and began to scrub his hands.

The water was boiling hot, but Gaster didn’t seem to notice as he scrubbed away the blue soul essence that clung to his bones. 

Even after all traces of the substance had been washed away, he didn’t stop scrubbing. He didn’t stop scrubbing until it hurt. Until it _really_ hurt. Only then did he turn off the faucet and towel his thoroughly scalded hands dry. When he was done he turned and started walking back towards the examination table. 

He didn’t make it. 

As he walked, his movements became more and more staggered until he could no longer keep upright and he fell hard onto his hands and knees. Gaster gasped and his pupils constricted until they were but mere pinpricks in his dark sockets. What did he just do? Did he just _hurt_ Sans? 

No… no that couldn’t be right, he had control! He had been so confident in his ability to suppress his determination there was no possible way his control could have failed! Gaster slammed his fist against the white tiled flooring. 

This wasn’t supposed to be happening. The Determination tablets were supposed to be making him stronger! They _were_ making him stronger. He lifted up his fist to reveal a small indent in the previously unmarred floor. His strength has increased exponentially over these past few months, but was this increase in power costing him his sanity? He was certainly losing something. Whether it be his moral compass or the entirety of his mind he was unsure. 

Gaster cringed and touched the crack above his right eye. He had a terrible headache. 

He also didn’t have much memory of what happened after he lost control. He only had small flashes of disjointed images, but it didn’t take a genius to figure out he had hurt Sans. He had promised his assistant after the last time he touched his soul that he wouldn’t touch it again without his permission. So finding himself holding Sans’ spent soul over his unconscious body was definitely not a good sign, to say the least. 

He had never lost himself for so long before. It would happen every once in a while when he worked on certain projects that meant a lot to him, but it would only happen for brief moments. 

Last week, for example, he had been helping Alphys with her robotics project when they became stumped by an issue with the hydraulic components in the robotic arm she was building. He had been reaching for a wrench one moment, and the next he found himself holding a screwdriver and Alphys was jumping up and down next to him commending him on his ability to fix the problem. He must have only blacked out for a few minutes, as far as he could tell, but somehow in that timeframe, he had managed to fix the issue with the hydraulics. 

He didn’t believe that the determination necessarily made him any more intelligent than he already was; rather it placed him in a state of mind that allowed him to more easily find a solution to a problem he was determined to solve. 

So then why did his determination latch onto Sans? What made his newest lab assistant a target?

He was about to get off the ground but stopped when he spotted a camera resting on the floor a few feet away from him. How curious! What was his camera doing here? He thought he had lost that thing over a month ago. Gaster grabbed the camera and noticed it was currently recording. If this camera had been recording during his black out, he might be able to gain some sort of insight into exactly what happened. 

He stopped the recording and played it back.

Boy, was that a mistake. 

The video hadn’t even been playing for more than a few minutes and Gaster already felt sick to his nonexistent stomach. He knew that he wasn’t the nicest monster in the Underground. He sometimes forgot to take other people’s feelings into account when he said or did things, and he also knew that he often had issues with reading emotions as well as expressing his own. However, what he saw in that video couldn’t possibly have been him. As callous as he may sometimes be, the Gaster he saw in this video was beyond unsympathetic, he was downright _cruel_. 

His actions in the video could best be described as predatory. He was manipulative, threatening, and abusive. The worst part of all was how apathetic he appeared to be during the whole thing. Like he just didn’t give a damn about how much he was hurting the younger, more vulnerable skeleton. 

Gaster had to look away from the screen.

He couldn’t believe it. Th-this wasn’t him! He wasn’t some kind of sociopathic freak! He… he wasn’t, right? He would never do something like this! But the feeling of doubt crept in as a thought wormed it’s way into his mind that there might actually be some small part of him deep within himself that mirrored what he saw on the camera’s screen. 

Maybe he really was a sociopath.

no. no. No. NO! 

Gaster dropped the camera and pressed his hands against both sides of his skull in some kind of desperate and futile effort to block out these awful thoughts. There was one question festering in his mind that frightened him the most. 

How dangerous was he? 

Tears escaped from his eye sockets and splattered onto the floor as he let out choked sob. Once it started he couldn’t stop it. Heavy sobs wracked his body as dark thoughts crossed his mind. Gaster’s breathing quickly became strained as he was only able to take in small gasps of air between each sob.

He hadn’t cried like this in a very long time. At least not since he witnessed his entire family get slaughtered by humans during the war. Now he began to wonder… were humans killing machines because they were slaves to their determination? Did they black out and hurt the people they lov- cared about too? Gaster didn’t think so. Determination must affect humans and monsters differently. 

He had to fix this. 

Once he was finally able to calm down, Gaster took off his glasses and used the sleeve of his lab coat to wipe the tear stains from his face. He had to stop this pathetic pity party. It wasn’t helping him and it wasn’t helping Sans. Right now he needed to focus on the most urgent issue at hand, which was Sans’ health status. 

Taking a deep breath, Gaster rose to his feet and made his way over to the examination table. 

When he peered down at the small, prone figure on the table, guilt immediately seeped through every fiber of his being. It honestly felt like he had been delt a critical blow to his soul. 

Skeleton heat be damned. Even if Sans still had the drug in his system, he didn’t deserve to be strapped to this godforsaken table any longer. Gaster quickly undid the leather straps and folded the armrests back into their upright position. 

He carefully held Sans up with one arm and pulled the smaller skeleton’s now sweat soaked, essence stained lab coat off of him and threw it into the corner of the room. He’ll have it incinerated later. 

Setting Sans back down, Gaster grabbed a wet rag and bowl from the sink and pulled his chair over to the table. Sans’ ribcage was covered in blue soul essence, and he most certainly was not about to let Sans lay in this filth for a moment longer. He soaked the rag in the bowl of warm water before running it down Sans’ sternum and across his ribs.  
As he worked, Gaster avoided looking at the expression on Sans’ face. It was rather disturbing to see Sans’ fixed grin while the rest of his facial features suggested tension and unease. 

When Gaster was done cleaning the sticky residue from Sans’ bones he could clearly see the full extent of the damage he caused. Sans was littered with contusions. The largest concentration of bruises was located around his neck and pelvis regions. 

He did this. He did this to Sans. He did this to a monster that only had 1hp. How close had he come to killing his assistant?

Gaster had never felt such self-hatred in his life. 

At this point the only thing he took solace in was the fact that he had not merged souls with Sans. After everything that has happened, he would have seriously considered throwing himself into the Core if he had forced Sans to merge souls with him. The act of merging souls was about as intimate as it can get, and to force someone into merging souls was one of the worst crimes a monster can commit. 

Gaster shook his head. He needed to stay focused.

He had a salve that could help heal the bruises but it was located down the hall in his private quarters. Yes, he had his own house in Snowdin, but as the Royal Scientist, he often had to stay at the lab overnight to work on time sensitive projects. Therefore, he had his own small living space right in the lab so he could have a place to rest and still remain close to the projects that required his attention. 

Gaster decided there was no way he was going to leave Sans by himself while he went to go get it salve. He was just going to have to bring him with him. He shrugged off his black lab coat and wrapped it tightly around Sans’ small frame. He then lifted him into his arms and headed for the door. One of his magic hands opened the door for him and a few more magic hands trailed behind him with the clipboard, camera, and Sans’ clothing. 

Gaster was thankful that no one was in the lab right now. He would have had no excuse should an employee have seen him walking down the hall clutching his naked, unconscious lab assistant to his chest. 

After taking a few twists and turns he eventually made it to his quarters and went inside.

The room was small and pretty much only consisted of a bed, a desktop computer, and a drawer full of spare clothing. It wasn’t completely uncommon for him to get dirty working on a project and he always appreciated having a spare set of clothes nearby. 

He placed Sans on his bed and went and retrieved the salve and some bandages from his bathroom. The bandages were just to help keep the salve on Sans’ bones and prevent it from accidentally getting wiped off. 

He sat on the edge of his bed and unscrewed the light blue lid from the small, white container. He placed the lid on his nightstand before dipping his phalanges into the colorless, warm goo. The salve was warm because it was infused with healing spells. 

As carefully as he could, he applied the clear healing agent to the injuries. Thankfully the bruising wasn’t too severe, but Gaster still applied a generous amount of the salve just in case. He also observed that Sans’ wrists were pretty bruised from him struggling against his restraints. Gaster felt his soul vibrate with anguish, but he steadied himself and continued to apply the salve. 

When he was done patching the smaller skeleton up, he grabbed the gray comforter from the end of the bed and covered Sans with it before heading back to the bathroom with the salve and bandages. 

Before he entered the bathroom he glanced back at Sans and was relieved to see that the tension in his face had eased slightly. That was a good indicator the salve was already working its magic. 

After Gaster placed the items back into the cabinet, he washed his hands at the sink. He looked up at his reflection in the mirror and acknowledged the fact that he looked like shit. He took off his glasses and splashed water onto his face while thinking about how awful this night has been.

Too bad he had no way of knowing it was about to get a whole lot worse. 

Dabbing at his face with a towel he looked back up at the mirror and immediately halted his movements. The light in his right eye socket was purple. He wasn’t using any magic right now, and even if he was, both eye lights would have been purple not just one of them. He dropped the towel into the sink and pressed the tips of his fingers against the mirror’s smooth surface.

Gaster noticed that his reflection had a flat affect and he ran his hand across his face to find much to his own surprise, that he too was suddenly lacking emotion. The image in the mirror didn’t change to reflect his surprise. His reflection slowly lifted its right hand and he became alarmed when he realized that his own right hand was raised. 

He watched as his reflection moved the hand down to his front pants pocket. Gaster ripped his eyes away from the mirror and looked down at his own hand resting against his pocket. Perhaps the most frightening aspect of this was the fact that his movements felt entirely voluntary. 

He could feel something small within the pocket. He reached in and extracted whatever it was and held it up so he could inspect the item.  
It was a very tiny vial that held a clear, red liquid in it and…

…

It was the antidote. 

It was the antidote to the skeleton heat.

He had the antidote to the skeleton heat in his pants pocket this whole time. 

He let the vial slip from his grasp and roll into the sink as he grabbed both sides of the counter for stability. For a brief moment he thought he was going to pass out as memories he didn’t remember having invaded his mind.

In one memory he was sitting at his desktop computer. He had just hacked into Sans’ medical profile and was reading about his hp related sleep issues. This memory took place about a month ago, but how was that possible? He had only just heard about Sans’ issue today when he had caught Sans sleeping on the job. 

A new memory jumped into his mind and in this one, he was labeling his newest experimental drugs. Everything seemed in order. He properly labeled both the sleep aid and skeleton heat drug correctly, but as he stood up to bring the tray of flasks over to the cabinet and put them away, he paused and ripped the labels off of the two drugs and switched them. Why the hell did he do that? 

One memory was basically just him hiding the camera from himself, as bizarre as that sounds.

Another memory was brought into focus and it was of him slipping the antidote into his pocket because he was unsure if Sans would take well to the drug, and the antidote was necessary in case Sans had a bad reaction. 

Gaster’s eye sockets widened as the pieces to the puzzle began to fit together. This was a setup. It was a meticulously calculated plan that took well over a month to complete. He had been blacking out far more often than he realized, and during the times he had lost control his determined self had apparently been busy. 

Gaster now understood the _how_ but he still didn’t understand the _why_. 

So he did the only thing he could think of. He glared up at his reflection in the mirror and asked, “Why? Why go through all this trouble just to hurt Sans?” 

His reflection glared back at him and said, “I didn’t do this to hurt Sans.”

Huh, he uh… wasn’t actually expecting to get an answer.

“Then why?” he demanded.

“Because you desired him, and that desire turned into determination as you were determined to have him.” Gaster was fully aware that these answers were coming from his own mouth. He really must truly be insane to be standing here having a conversation with his own reflection!

“I do _not_ desire Sans.”

His reflection laughed. “Why are you lying to yourself?” 

Good question. Why _was_ he lying to himself? It was true he had desired Sans for a few months now. He found the smaller skeleton to be absolutely brilliant! He thoroughly enjoyed discussing projects with Sans and always valued his input. His assistant was also very witty and managed to keep him grounded when he felt himself slipping away. A joke from Sans was all he needed to bring himself back reality whenever he got pulled in too deep into his work. 

Gaster rubbed the back of his skull and said, “Fine, I’ll admit that I feel affection towards Sans, but I had no right to take him like that. I would never want that!” He was progressively becoming angrier at the selfish being in the mirror. 

“It doesn’t matter what you want. The only thing that matters is what you are determined to do.” 

Determined! Determined! Determined! Gaster was getting sick and tired of Determination. 

“That’s it then… isn’t? Effective immediately I’m going to cease taking the Determination tablets.”

His reflection burst out laughing at that. “No, you won’t. You need the tablets to increase your strength so you can free the monsters from their underground exile. Monsters are starting to lose hope and if you can’t free them from this underground hell it will be their tomb.” 

“Shut up.” He growled. 

“Without Determination you are weak and foolish, just completely useless!” 

“I said shut. up!” His magic was crackling ominously around him.

“You are nothing but an inferior monster who couldn’t even save his own family and now you’re going to let all of monsterkind die-“

“ENOUGH!” Gaster screamed, and the mirror exploded showering him with glass. He had to bring his arms up to protect his face from the flying shards. 

When the glass stopped flying he brought his arms down and was shocked to see a bone protruding out of the wall where the mirror had been. He didn’t mean to conjure a bone, but he had just gotten so damn angry. Gaster slowly backed up until he hit the bathroom wall and being mindful of the glass he lowered himself down to the floor. 

He brought his knees up to his chest and buried his skull into his arms.

He… he just needed to catch his breath for a moment and reflect –no pun intended- on all that has happened tonight.

When he did eventually stand back up ten minutes later, Gaster grabbed his glasses off the counter and placed them back onto his face. He looked down at himself and was disappointed to see that his favorite white turtleneck had a bunch of holes in it from the glass shards. He walked out of the bathroom and pulled the destroyed top over his head and flung it haphazardly into his closet.

He was absolutely exhausted and didn’t even bother putting on another shirt. Instead, he just sat down in his computer chair and watched the rise and fall of Sans’ chest. At least he appeared to actually be sleeping now instead of being stone cold knocked out. 

Gaster sighed and felt his own eyelids starting to droop.

Not even five minutes later he was slumped over in his chair, fast asleep.

**Notes for the Chapter:**

> It's 3:30am here. can I sleep yet? So sleepy...
> 
> Once again feel free to comment! I love reading your comments.


	7. Dream of Dark Places

Something smelled wonderful. Like chemicals and ozone… like _Gaster_. 

Sans sighed and rolled over, trying to bring himself closer to the intoxicating sent. Why did it smell like his boss? Did he ‘accidentally’ take Gaster’s scarf home with him again? It's happened once before. After work one day he had grabbed his coat off the coat rack and ‘accidentally’ grabbed Gaster’s scarf as well. He may or may not have been a total perv and fell asleep that night clutching the gray scarf. 

Heh, he was such a bonehead. 

Sans yawned and stretched. It had to be almost time for his bro to come barging into his room like he does every morning and announce what a great day it’s going to be because he, The Great Papyrus! is going to make it great! Sans has Papyrus’s whole morning monolog memorized. His bro was so cool to greet him each and every day like that. Sans smiled and rolled onto his back and opened his eyes.

…

Welp, this was definitely _not_ his room! It was far too dark to be his room. Sans sat up and looked around. The room had no windows so there was no source of natural light. As his eyes adjusted to the darkness, he looked down he saw he was wearing Gaster’s lab coat. Well, that would explain the smell alright. Sans ran his hand over the black coat. Where the heck was he and why was he wearing the Royal Scientist’s lab coa- "urgh!" Sans grunted as all the memories from last night came flooding back into his skull and he remembered _everything_. 

Sans growled and blue magic flared out of his left eye socket as his anger spiked. How could Gaster do this to him? He had been nothing but loyal to the bony bastard and this was how he repaid him? Sans put his face into his hands and groaned. Had he been a fool to trust the scientist? 

No… he could never have predicted that Gaster would do something so low.

Sans shook his head and took a deep breath to calm himself down. First, he needed to acknowledge the fact that Gaster might not have been himself when he decided to… decided to... Sans felt disgusted. He really didn’t want to think about how he had been violated by the older skeleton. He was just so confused. He had no idea what was going on anymore. 

Did Gaster really go insane when he while he was on the table? Was he still insane? Why did his magic change colors when he went crazy? Nothing about any of this made sense!

The anger he felt faded and fear took its place. What if Gaster still wasn’t himself and he was lurking around here preparing another attack? 

With the help of the soft blue glow that was emitting from his magic eye, Sans looked around the room. The light only helped a little and he still couldn’t see very far, but to his left he could just make out what appeared to be a nightstand. Neatly folded on the nightstand was his clothing. Well, he thought to himself, if he decided to book it out of here at least he won’t have to run home in his barebones! 

Sans reached up to rub his aching neck but paused when his fingers made contact with a soft, cloth-like material. Someone had bandaged him up. That was a good sign, wasn’t it? It was probably Gaster, and that could mean he was back to his old self, right? Or maybe he was still insane and just wanted to keep him alive and healthy so he could attack him again. 

Now wasn’t _that_ a frightening thought? 

Instead of using any more of his dim magic to look around the room, he reached up and turned on the lamp that was also sitting on the nightstand. 

The light blinked on and Sans almost cried out in fright. He had to immediately cover his mouth with his hands to prevent any noises from escaping.

Sitting directly in front of him in a black leather computer chair was none other than the Royal Scientist himself. The older skeleton appeared to be sound asleep. Sans slowly lowered his hands and observed the sleeping skeleton. Gaster looked exhausted even in his sleep. 

It was also really strange to see him with so little clothes on. Gaster was the kind of guy who wore layers on even the hottest summer day. Actually, now that he thought about it, he had never seen Gaster without his lab coat on before. The man always wore it like a protective shell. Without it, the tall skeleton looked almost vulnerable. _Almost_. 

Even while he slept, power practically oozed off the Royal Scientist. There was no doubt in Sans’ mind that Gaster was one of the strongest monsters he had ever encountered. He wouldn’t be surprised if the powerful skeleton monster could hold his own in a fight against a boss monster or even a human. 

Sans spotted strange cracks running along Gaster’s ribs. It kind of looked as though Gaster has fought in battle before with wounds like those.

Before Sans started working at the lab he had attended New Home University, which is located in the capital where he and Papyrus currently live. While he was attending class there, a nasty rumor circulated around campus that Dr. Gaster, the famous Royal Scientist, refuses to enter the Hall of Judgment. 

The Hall of Judgment was the only place a monster could see another monster’s LV. The rumors suggested that Gaster didn’t enter the hall because he had an unusually high Level of Violence for a monster. Sans used to dismiss those rumors as being fraudulent, but now he wasn’t so sure. Gaster was definitely powerful but was he powerful because of his LV?

Sans watched the sleeping skeleton carefully. He was fully prepared to bolt at the first sign that Gaster still wasn’t himself. He absolutely would not survive an actual battle with Gaster.

Thankfully the first sign Sans received was one of hope as the older skeleton abruptly shoved his thumb into his mouth and started snoring. 

Sans almost choked trying not to laugh. Yup, this was _his_ Gaster alright. Oh my god, he still couldn’t believe this guy actually slept with his thumb in his mouth! Relief washed over Sans and he slumped back against the pillows behind him. 

So now what should he do? Sans closed his eye sockets and thought about his options. Should he get dressed and run as fast as he could away from this place and never return? Or should he wait for Gaster to wake up and demand an explanation? 

Sans was a stubborn skeleton. When he wanted something he could usually find a way to get what he wanted, and right now he wanted a goddamn explanation and he wasn’t going to leave until he got one. He wasn’t sure if he could bring himself to wake Gaster up himself, though. As much as he hated to admit it, he was scared. He was scared of Gaster whether he was normal or not.

Sans heard a low pitched moan and his eye sockets shot open. He sat back up again and observed Gaster whimpering and twitching in his sleep. Was he having a bad dream? 

After last night’s events Sans wasn’t feeling very charitable, and it didn’t help that he was a bit frightened by the sleeping skeleton. Even if Gaster wasn’t himself when things went to shit, he couldn’t help but feel that the scientist was still responsible in some way for what happened last night. Sans flopped back down onto the mattress and put a pillow over his head to block the noise. 

Let the idiot have a nightmare, Sans thought coolly. 

………………………………………………………………………………………………….

Dark… it was so very dark. 

No matter which direction he walked in there was only darkness. It didn’t matter for how long he walked in one direction, nothing ever changed. There was no sound other than the sound of his own footsteps, and despite how open and vast the darkness seemed, when he yelled there was no echo. There was no sky and there was no ground, there was only black. 

He’s had this dream before. He’s had this dream 78 times before to be exact. It’s always the same. He’d walk for what felt like hours in this endless void and then he’d wake up. It was boring and pointless. 

He’s tried to wake himself up during the dream before but nothing ever seemed to work. After a while, he stopped trying and found that letting the dream run its course was the fastest way to get it to end.

So here Gaster was, once again for the 79th time, walking aimlessly through the darkness. He was beginning to think that the oppressive darkness was starting to get to him. Even though he’s had this same dream over and over again, his discomfort seemed to increase each time he had this dream. This time around it felt… tense. 

Gaster came to a stop. He looked over his shoulder, squinting at the infinite darkness that lay behind him. Nothing, there was nothing there. Gaster shook his head. The tense atmosphere seemed to be causing him some minor paranoia. Gaster was about to resume walking when he heard something ringing.

This was new. This was something that had never happened in the dream before. 

Gaster looked around and spotted the source of the ringing. 

Three feet away from him was his cell phone, lying face down on the ground. How strange! He walked over to it and contemplated whether or not he should pick it up. Cursing his naturally curious mind, he picked the phone up and turned it over. 

There was some kind of strange black goop on the screen. 

Gaster face scrunched up with disgust as he touched it and rubbed the black ooze between his fingers. This is… odd. It looked like black ink but it felt much thicker than that. Gaster used the hem of his lab coat to wipe away the sludge. When it was clear he looked at the caller ID.

UNKNOWN NAME

UNKNOWN NUMBER

This was starting to look like a cheesy horror film, Gaster mused. Not the least bit intimidated, but very intrigued, he pressed the accept call button and held the phone up to his skull.

“Hello?” 

*CRACKLE* -KSSSSSSSSSSSssssssssssss- 

It was nothing but hissing static. 

“Hello? Who are you? Can you hear me?” 

A voice emerged from the white noise. 

-KSsssssssss- **WATCHING. YOU. FROM. _THE VOID_**. –KSssssssss- *Click*

A shiver ran up Gaster’s spine. He recognized that voice. Even though the voice was broken and garbled by the static, he knew exactly who that voice belonged to.

This wasn’t happening! It’s just a dream, he told himself.

The phone fell from Gaster’s hands and smashed to pieces on the ground. He spun around looking for evidence that someone was watching him. He spun around again, and again, looking in every direction but there was nothing. 

"I’m not amused by these games,” he said to no one in particular. 

His paranoia was chewing away at his calm resolve and fear bubbled to the surface. He could feel eyes on him from every direction. Panic finally took hold of him and he started running as fast as he could. It didn’t matter that he had no idea where he was going. All he cared about was getting away from his present location. Getting away from that haunting voice. 

He didn’t want to be here. He wanted to wake up! Why couldn’t he wake up? 

With his mind fogged with panic, Gaster didn’t notice the ground beneath his feet was beginning to distort, and becoming more and more uneven until one moment he was running on solid ground, and the next he was slogging his way through black ooze. It was the same black ooze he had found on the cell phone.

The black sludge was up to his knees and its viscosity limited his range of movement considerably. 

Gaster cringed. It was so thick and slimy. Disgusting! It felt disgusting!

Panting, Gaster came to a complete stop. He couldn’t continue on like this, the strange liquid was too thick to traverse through. He was just wasting energy.

As Gaster caught his breath he looked around. The black ooze shimmered like the surface of a lake and seemed to extend as far as his eyes could see.  
What was this inky black substance? 

Against his better judgment, he bent closer to inspect the inky black slime. Just as his fingers were about to touch the surface of the liquid, a black tendril shot out of the ooze and wrapped around his wrist before he could pull away. 

“What!?” Gaster gasped.

He tried wrenching his arm out of its grasp, but it was fastened on tight to his wrist. He couldn’t get it to budge even an inch. As he struggled with the tendril on his wrist, a second slimy black tendril flew out of the inky ooze and wrapped around his midsection. 

Gaster could feel the thick ropes of black sludge attempting to pull him into the pool of ooze. “No! Release me!” Gaster cried. Another one coiled around his other arm and another shot up out of the ooze and wrapped around his neck. 

The ropes of black slime pulled Gaster onto his knees. He stiffened as he felt a tendril slither into his eye socket.

“AH! S-STOP! P-P-PLEASE! TH-THAT HURTS!!” Gaster was almost fully submerged into the ooze now. He could feel it consuming him. Black slime was squirming in his ribcage, in his skull, and even in his mouth. It was killing him! 

Terrified he yelled, “HELP! HELP ME SOMEONE! ANYONE! FOR THE LOVE OF GOD, HELP ME PLEASE!”

But nobody came.

**Notes for the Chapter:**

> Hmm... I wonder who that person on the phone was? 
> 
> Sorry this chapter was so short! I just got a full time job now so that's eating up most of my time. :(
> 
> Getting tired of the angst? I need a show of hands. How many of you want some fluffy smut? Can't promise any for the next chapter, but really soon if you guys want some. :3 Unless ya'll wan't these babies to suffer more? I can make that happen too. >:D


	8. A Damn Good Explanation pt. 1

There wasn’t a pillow in the world that could block out these pained cries. 

Sans threw the pillow off of his head and sat up. He hadn’t wanted to help Gaster out of fear and spite, but the man sounded like he was in real physical pain. Sans wasn’t heartless… well… he _was_ heartless technically, but that’s not the point! The point is that he wasn’t a sadist and he didn’t particularly enjoy hearing the sounds of someone suffering. 

That didn’t mean he wanted to actually go over and wake Gaster up, though. 

First he tried throwing his pillow at the sleeping skeleton, but just completely missed because his aim freaking sucks. It’s not his fault! He wasn’t allowed to participate in combat training in school because of his low hp, so his accuracy was abysmal. 

Next he tried shouting at Gaster to wake up, but that just made the man groan louder. It also kind of made Sans feel like a jackass for shouting at an unconscious person in pain, so he stopped. Eventually, Sans decided to try to grab Gaster’s soul with his blue magic in an attempt to magically shake him awake but for some reason, the soul kept slipping through his grasp. All out of ideas, Sans only had one option left.

“i can’t believe i’m doing this,” Sans grumbled as he swung his legs over the side of the bed and slowly lowered himself to the floor. Once he was standing in front of Gaster, he hesitated before grabbing the distressed skeleton by the shoulders. 

“hey, wake up old man.” Sans gently shook Gaster. The other skeleton whimpered and tried pulling away from Sans. “oh come on doc, don’t be like that.” Sans said raising his voice slightly. “i’m trying to help you!” He watched but remained unmoved as Gaster weakly struggled against him. Getting impatient, Sans shouted, “wake up! wake up you idiot, it’s just a dream. it’s okay, you’re safe!” Sans shook Gaster roughly. 

Gaster’s eye sockets suddenly shot open and he let out a frightened yell.

“AAAHHHHH!!!”

“aahhhh!”

-CRACK!-

Startled by Gaster’s yell, Sans let out his own yell of surprise and instinctively lashed out. His left fist collided with Gaster’s jaw, sending the Royal Scientist to the floor. 

Curled up on his side on the ground, Gaster held his jaw and swore loudly in his native Wingding language. 

Oh man, oohhhhh man… did… did he really just punch Gaster in the face? Well shit, that could have gone a whole lot better, Sans thought as he rubbed his knuckles. 

Gaster stopped groaning and sat up looking a little dazed.

“are you okay doc? i… i didn’t mean to do it. i thought you were going to attack me or something,” 

Gaster held up a hand, signaling for Sans to wait a moment. He then pulled hard on his jaw until there was another loud cracking noise. He opened and closed his mouth a few times testing the adjustment before turning to his apologetic assistant. 

“Sans, you have an _excellent_ left hook.”

Looking a bit sheepish, the smaller skeleton closed his left eye socket but kept the right one open and said, “uh… yeah, it’s probably because i drink a lot of _punch_.”

Gaster snorted and pulled himself back up into his chair. “Odd, because all I ever see you drink is coffee and ketchup.” 

“look doc, i’m real sorry about clobbering you in the jaw.” Sans really didn’t mean to punch Gaster, he had just gotten spooked and for a moment he seriously thought Gaster was going to attack him. 

Gaster turned away and glared at the floor. “Don’t apologize Sans, please.” Gaster rubbed his jaw. “I probably deserved it for what happened last night.” 

At the mention of last night, the anger Sans felt when he first woke up returned and he clenched his fists. “yeah, about that. i think it’s time you told me what the hell is going on, and you’d better have a damn good explanation if you don’t want me to call the Royal Guard.” Sans immediately winced at his own words. He shouldn’t have mentioned he was thinking about calling the Royal Guard. If Gaster wanted to, he could easily dust him for making threats like that. After all, the only one who would really miss him if he died was Papyrus. 

Gaster made direct eye contact with Sans and said firmly, “If you want to turn me over to the Royal Guard for what I did, I will support your decision to do so. What I did to you was unforgivable… _barbaric_.” Gaster placed his hand on the center of his ribcage and said, “I feel pain in my soul knowing that I’ve hurt you in such a way. Please Sans, even if I provide you with ‘a damn good explanation,’ as you put it, do not hesitate to call the authorities if that’s something you still desire to do.”

Sans didn’t know what to say to that. He scanned Gaster’s face for any signs of insincerity but found nothing of the sort. It seemed to Sans that Gaster was making a strong effort to make him feel safe. He appreciated the gesture. 

Gaster appeared to be waiting for a response so Sans just nodded and mumbled, “ok.” 

“Good. Now, before I begin I have to ask, how are you feeling?” 

Feeling? He wanted to know how he was _feeling_? He was feeling a lot like hot garbage actually, but did he want Gaster to know that? Would showing weakness endanger him right now? Part of him didn’t want to tell Gaster anything but if Gaster was making an effort, Sans supposed he should try to make one too.  
Sans looked away and fidgeted his hands anxiously. “i dunno, i guess i’m feeling angry, hurt, confused, um maybe a little freaked out-“

Gaster paled significantly and quickly interjected. “N-no, you misunderstood. I meant how are you feeling physically? You’re not feeling feverish anymore, correct?” Hearing about Sans’ emotional damage was almost as distressing as seeing the physical damage. 

“no. i’m alright, just a little achy.” 

Gaster nodded his head slowly. “I’d feel better if you remained in bed for a little while longer. You weren’t in a very good state last night when I… when I found you, and I put a healing salve on your injuries. The salve will work better if you’re relaxed.” 

Sans kind of wanted to remain standing in case he needed to make a quick exit but he was also still feeling fatigued. Not wanting Gaster to know how tired he was, he decided to take this opportunity to negotiate. 

“if i get back into bed, you have to promise me that you’ll tell me everything. no lies and no leaving out any important details.” 

Gaster hesitated. This was… complicated to say the least. He would be breaking a lot of promises if he told Sans everything. However, he absolutely owed it to him after what happened last night. Keeping him in the dark would be completely unfair and wrong. 

After weighing his options, Gaster relented. “Alright Sans, if you want to know everything I’ll tell you everything.”

Sans gave him a small appreciative smile before climbing back up into bed. Gaster dragged his chair over so he could still be face to face with Sans and sat down.  
Gaster immediately jumped into his explanation. “What I’m about to tell you is extremely classified. In fact, I was required to take a royal oath forbidding me from speaking of this to anyone other than Asgore or Alphys.” 

Sans gave Gaster a perplexed look. “alphys? alphys from engineering? what does she have to do with anything?”

Gaster took a shaky breath and said, “Everything. She has to do with everything. It was just an accident, dammit! She didn’t mean to do it!” Gaster slammed the palm of his hand down on the nightstand causing Sans to jump a little. Gaster then clenched his eye sockets shut and held up both his hands. “Hold on, I’m getting ahead of myself.” He reopened his eye sockets and said, “Sans, what do you know about human souls?” 

Sans thought for a moment and said, “well i know they last longer than monster souls and they can provide monsters with incredible power if they are absorbed. I also know that the king needs 7 of them to free us and so far we have 5.”

“Very good, you were paying attention in school, but can you tell me how many _years_ it’s been since the last human soul was collected?” 

Sans tapped his chin in thought. “it has to have been almost a century since the last human was spotted down here, right? Jeez doc, if i had known i was going to get quizzed on humans i would have _boned_ up on the subject.” It was an awful attempt to lighten the mood, and he swallowed thickly as Gaster shot him a disapproving glare.

“It has been exactly 97 years, 4 months, and 23 days since the last human soul was gathered by the King.”

“oh uh, wow. that’s just something you know off the top of your head, huh?” 

Gaster ignored him. “Have you heard any reports about monsters _falling down_ , Sans?”

Confused as to where this was going, Sans asked, “what does any of this have to do with what happened tonight?” 

“I’ll get to that, just bear with me and answer the question,” Gaster said dismissively. 

Yes, Sans had heard the reports. In fact, one of his next door neighbors had fallen down last week. The poor bastard was found by his kids when they came home from school. Each week it seemed someone new was struck with the mysterious illness. 

“yeah, i’ve heard the reports. Monsters all across the Underground are falling into a coma-like state, and according to the news, none of the experts can figure out what’s causing this strange illness.” 

Gaster flashed a dismal smile and said, “Yes well, that’s what the news outlets have been told to tell the public. The truth is that we know exactly what’s causing the illness, but if word got out about what was really transpiring there would be total chaos. Asgore himself had to impose an information embargo on the media regarding anything that has to do with illness. Unfortunately, such a restriction on information draws a lot of attention. Suddenly every junior reporter in the Underground thinks they’re a top notch detective who can weasel the information out you.”

Gaster shook his head in disgust. “They are incredibly annoying and have no idea how much danger they would put the Underground in if word got out about the true nature of the illness.” 

Gaster got sidetracked on a tangent about nosy journalists and Sans just couldn’t take it anymore. He needed to know the truth. Why was the cause of the illness so important that it warranted a government cover-up? And most importantly, was he or his brother at risk? Sans could already tell he wasn’t going to like the answer. 

“gaster,” Sans called sharply. The older skeleton snapped out of his ravings and looked over to Sans. “i gotta know doc, what exactly is causing monsters to fall down? what is so awful about this illness that it required the government to step in and censor the press?” 

Gaster ran a hand down his face and sighed. 

“The cause of the illness is hope Sans, monsters are losing hope. Overcrowding, lack of real sunlight, never ending monotony... This exile from the surface world is taking its toll on monsterkind. Monsters need hope to survive, and without it, they stop functioning. Total loss of hope can cause a monster to ‘fall down’ and go into a coma-like state as you mentioned earlier, but that’s not the end of it. Eventually the monster withers and dies. Even round the clock care can only prevent the inevitable death for so long.”

Gaster wasn’t looking at Sans anymore. He was staring off into the distance. He wasn’t looking at anything, but he was seeing _everything_. “Don’t you see Sans?” he whispered. Don’t you see now why the public cannot be told of this? The loss of the King’s children, the abandonment of Queen Toriel, these are all nails in Monsterkind’s coffin. This new information will just be another nail and I’m convinced it could be the last nail needed before…” Gaster trailed off, switching his attention back to his assistant.

“Sans, we are on the precipice of an Extinction Level Event for monsterkind, and there is almost nothing we can do to stop it.”

That single sentence was easily the one of the most devastating things Sans has ever heard in his life. 

Sans was in disbelief. “no way… that can’t be true, what about Asgore? once he gets all 7 human souls we’ll be free!”

Gaster grimaced. “We are all out of time. The last soul was collected exactly 97 years, 4 months, and 23 days ago. I’ve ran the numbers through simulations and they’ve projected that we have less than 50 years until the number of monsters stricken by the illness reaches catastrophic numbers.”

Fifty _years_!? Fifty years was nothing to a monster! Gaster himself had to be almost a thousand years old, same for Asgore. Boss monsters, skeleton monsters, rock monsters, ghost monsters, as well as a few other types of monsters can live to be over two thousand years old. Typically monsters that had a more organic quality to them such as animal monsters or plant monsters lived between five hundred and a thousand years old. 

Gaster’s expression grew darker. “And Sans? Those numbers are based on the assumption the public never finds out about the cause of the illness. I suspect that we will have even less time should word get out. 

Sans felt sick. “wow doc, this is bad. this is really really really bad.” 

“Yes, and now that you understand the gravity of the situation I want you to know that there’s a possible cure.” 

Sans instantly perked up and smiled, “what? why didn’t ya say so? that’s great!” 

Gaster didn’t say anything but he didn’t need to because the expression on his face said everything for him. Sans’ smile fell. “what’s wrong?”

“This is also highly sensitive information, so listen carefully because I’m not going to repeat it.” Sans nodded and Gaster continued, “I have found that human souls are made out of a substance I call Determination or DT for short. DT is what makes humans so unbelievably powerful. I believe the cure to the falling down illness can be found within this substance. It is my belief that with the right dosage, Determination can be given to monsters as a substitute for hope.”

Gaster adjusted his glasses and looked away. “After I discovered this, I brought my findings before the King, who then provided funding and the human souls for experimentation. Alphys, who was my personal assistant at the time, and I were sworn to secrecy.” 

Sans was so confused. “wait, so you’re telling me that alphys was your personal assistant before me? how come no one has ever mentioned that to me before? I pass her in the halls almost every day!” 

Gaster sneered and said, “I’m going to be blunt with you Sans. The reason no one told you is because it was none of your goddamn business!" Sans was shocked by Gaster’s tone, and apparently so was Gaster because the sneer dropped from his face and he groaned and pinched the bridge of his nasal cavity. “I’m sorry. This particular subject is rather difficult for me to talk about.”

After taking a minute to regather himself, Gaster continued. “After we extracted some DT from the souls Asgore had collected, we began our experiments. It was a complete disaster from the beginning. Due to the urgency of the situation, we began DT/monster experimentation trials immediately. We received our first monster that had fallen victim to the illness. He was just some old rabbit monster named Binny, who had been living on the streets. No significant other, no children, no family. He was a perfect candidate for DT testing.” Gaster smiled sadly.  
“  
I didn’t know what would happen when I injected the DT directly into his soul. I thought that one syringe of DT wouldn’t be enough to wake him up and I was prepared with 3 extra syringes full of DT so I could add more as needed.” Gaster laughed bitterly. “Haha… I injected the soul with DT, completely emptying the syringe. As soon as I pulled the syringe out of his soul he burst into dust.”

Sans gasped and Gaster continued to laugh but it was becoming increasingly hysterical. “Haha! I… I’m pretty sure I was picking bits of Binny dust out from between my finger joints for a full week after that… Hahaha! P-poor Binny!” Sans was seriously becoming concerned for Gaster’s sanity. “h-hey doc, stay with me alright? we don’t have to talk about the old rabbit monster anymore.”

Gaster stopped laughing and said, “I wish I could say we stopped testing DT on monsters after that, but of course we had only just begun. After awhile the test subjects stopped turning to dust and I thought we had hit a breakthrough. Some of the subjects even started waking up and walking around!” Gaster smiled at the memory. “Alphys and I were prepared to tell everyone the great news.” Gaster’s smile vanished in an instant. “But then they started to melt.”

“melt!?” Sans exclaimed in horror. 

Gaster nodded. “Unfortunately, since monster bodies don't have enough physical matter to handle the DT, the magic that composed them lost cohesion. It was awful. Their cries of pain were just god awful. It’s a good thing we kept them separated, as I could only imagine what would’ve happened had they been together when they melted.”

“what happened to them after that? i haven’t heard any reports of monsters that had fallen down getting returned to their families as melty monsters.” 

“Don’t be ridiculous Sans, I couldn’t let them leave like that so I destroyed them.” 

There wasn’t an ounce of remorse in Gaster’s voice. Sans shivered before shouting, “how can you talk about killing so many monsters so nonchalantly when you seemed so shaken up about accidentally killing that old rabbit monster?” 

Not meeting Sans’ gaze, Gaster shrugged. “I guess it just got easier with time.”

Sans couldn’t believe what he was hearing. “that’s disgusting,” he whispered.

Gaster’s eyes snapped up and locked with Sans’. “Don’t you dare fucking judge me, boy,” he snarled. “I did what I had to do. What I was _ordered_ to do. Do you think I enjoyed it? Executioner wasn’t exactly in the job description when I applied for this position!” Gaster cried before slumping into his chair. He let his head fall into his hands. “You know… as bad as it sounds, I don’t regret experimenting on those monsters. After all, the needs of the many outweigh the needs of the few. What are a few dozen deaths, if it helps you find a cure that could save thousands of lives?” 

Sans scowled. “but by the sound of your story you _haven’t_ found a cure yet.” 

Gaster smiled and held up a finger. “Ah, but that’s where you’re wrong. I believe it’s time I told you the second part of this story. The part where I became _Determined_.” Gaster touched the crack above his right eye.

Sans’ eye sockets widened as a wave of realization hit him and he felt dread in the pit of his nonexistent stomach. “oh no. doc, c’mon… please tell me you didn’t do what i think you did.” 

“What is it that you believe I did, Sans?” Gaster asked with curiosity. 

Sans could feel his anger rising. “i think,” he said hotly, “that you were being an idiot and injected yourself with DT!”

Gaster chuckled. “Well, I can’t deny that I was being an idiot at the time, but no, I did not inject myself with DT.”

Sans sighed with relief. 

“It was Alphys who injected me with DT.”

**Notes for the Chapter:**

> The explanation was getting too long so I'm splitting it into two parts. At least it shouldn't take me too long to finish pt. 2.


	9. A Damn Good Explanation pt. 2

Sans felt his soul heave within his ribcage. 

“why the heck would she inject you with DT? she doesn’t exactly seem like the kind of monster that just goes around jabbing their boss with syringes… unless killing innocent monsters caused her to go out of her mind too.” 

Sans wanted his words to hurt and by the look of horror and pain Gaster was currently emoting, he had succeeded. 

“Sans, that’s quite enough,” the scientist growled. “I would never allow Alphys to harm a monster for the sake of research, no matter how important that research was. That was my burden, and my burden to bear alone. I only started letting her inject DT when I was absolutely certain that they wouldn’t turn to dust directly after injection.” 

Alphys was a good monster. When the monsters they had injected with DT had liquefied, she even tried to convince him that they should be allowed to live because they were still capable of _thoughts_ and _feelings_. It was a noble effort on her part that displayed the type of compassionate monster she truly was. It was a futile effort, but a noble one nonetheless.

“I must insist that you do not place Alphys on the same level as myself. She doesn’t deserve that,” He remarked sternly. 

Sans hung his head in shame. Gaster was right. He didn’t know Alphys very well, but from what he’s seen of the small yellow lizard, Alphys was a meek and nervous monster. However, she’s been nothing but kind to him ever since he joined the team. 

“i’m sorry doc, that was completely uncalled for. i can’t even envision alphys doing something like that.” 

Gaster visibly relaxed. “You’re correct. She would never do something like that on purpose.” Gaster then stood up and walked over to his computer desk. Sans watched as the other skeleton grabbed something off a shelf. “She was an excellent assistant who could have one day even been my successor.” Gaster walked back to Sans and handed him the object.

It was a framed photograph. 

In the photo Alphys was standing next to a large machine, and standing beside her with a hand on her shoulder was Gaster. They were both smiling and Gaster looked so proud. Was this really Alphys? Sans had never seen her looking as confident as she appeared in this picture. 

“what happened?” Sans’ needed to know. He needed to know why Alphys was no longer Gaster’s assistant, he needed to know how exactly Gaster became Determined, and he needed to know how this all ties in with the way Gaster had behaved last night. There were just so many unanswered questions swirling around Sans’ mind, and he was already feeling a bit overwhelmed by everything he’s learned already. 

“An accident, it was just a stupid accident.” Gaster sat back down and folded his hands in his lap.

“After what happened to our first test subject, I decided that we needed to assign our future test subjects with numbers rather than names to help us… um.”

“forget that they’re real monsters?” Sans finished for him. “to help you overcome what i could _only_ imagine was an overwhelming sense of guilt?” His words were sharp as he still couldn’t understand how Gaster could knowingly subject helpless monsters to this sort of experimentation even if it was for the greater good. 

Gaster couldn’t bear to look Sans in the eyes. It was true. He had removed their names and assigned them numbers to make them less like monsters and more like objects. To make what he was doing to them hurt less for him. The name Binny was already seared into his mind and he didn’t want any more to join it. Was that so wrong? Was that _selfish_?

“Yes… yes, you’re correct Sans, and to further distance ourselves from the test subjects, Alphys and I designed a room where we could administer the DT without actually having to be in the room itself. It wasn’t just to distance ourselves, of course, we had… safety concerns.” Gaster frowned.

“In my spare time, I was also testing DT on non-magical creatures to get a better understanding of why DT affects magical and non-magical creatures differently. The rats I injected with DT suffered no negative physical effects, but they did become unusually aggressive. I was worried that even if we managed to successfully inject DT into a monster without them having any physical side effects, they might still become aggressive or even dangerous.” 

Gaster’s eye sockets widened marginally as he just now realized that the rats might have been aggressive because they had been _determined_ to escape at the time. Hmm… that’s something he’s going to have to remember to put in their files later. 

“I installed cameras that sent a live video feed of the DT experimentation room to our observation room across the hall. That way Alphys and I could monitor the experiments from a safe distance.” Gaster paused and looked to the smaller skeleton. “You’re a bright monster Sans, do you have any ideas on how we managed to inject DT into monsters whilst being in an entirely different room?”

Sans looked down at the photo in his hands. The answer was right in front of him. In the photo, Gaster and Alphys were standing next to a…

“machine. you guys built a machine that could inject monsters for you. heh, i’m willing to bet a year’s supply of ketchup the machine was hooked up to some kind of control panel in the observation room.”

The lights in Gaster’s eye sockets brightened and he smiled warmly. “Very good Sans, excellent! Yes, Alphys built the machine entirely by herself. The DT machine has a robotic arm that allows us to adjust its position whenever necessary. The most impressive feature, however, is its laser guidance system. We needed to be sure that the DT was being administered with pinpoint accuracy. With the laser guidance system and the maneuverable robotic arm, we were able to achieve just that. The machine was dubbed LG-DTG, Laser Guided Determination Gun, or DT Gun for short.”

The mention of a gun caught Sans’ attention. “so what? the machine can shoot DT or something?”

“No, not quite… well I mean it _could_ shoot DT if I tweaked a few things.” Gaster appeared to space out for a second. Suddenly, he yanked opened the drawer of the nightstand and extracted a tape recorder. He pressed the power button, held it next to his mouth and said in a completely professional voice, “Note to self, adjust DT Gun so that it can actually fire DT.” 

Still holding the recorder next to his mouth, Gaster then jumped out of his seat, jammed a finger into the air dramatically and shouted in a not so professional voice, “MAXIMUM FIREPOWER!” The shout at the end startled Sans and the smaller skeleton gave Gaster his best, what the hell is wrong with you, look. 

Gaster, seeming to realize that Sans was still sitting right there, coughed awkwardly. 

“Ahem, I’m sorry Sans. An idea struck me and I just couldn’t let it go. I mean, it doesn’t even _have_ to be DT. I could probably get it to shoot an injector full of any kind of liquid.” Gaster paused for a moment in thought before shaking his head. “Um, but perhaps this isn’t important right now,” he said as he tossed the tape recorder back into the drawer. 

The odd scientist then continued talking as if nothing had happened. “Actually, I would equate the DT Gun more so to a nail gun than anything else.”

Perhaps Sans should have been more concerned by Gaster’s strange outburst, but to be honest that kind of behavior was completely normal for the scientist. Gaster’s seemingly bizarre behavior reminded Sans that despite everything that happened last night, Gaster was still an idiotic dork. Sans smiled a little. It was actually kind of nice to see the Gaster he was used to. _This_ was the Gaster that gets himself stuck on the ceiling with an antigravity belt. 

Unfortunately Sans’ smile didn’t last long as Gaster grew significantly more somber. “It’s ridiculous. You would think that with our numerous safety precautions an accident wouldn’t have occurred, but I suppose that’s Murphy’s Law for you. Anything that can go wrong, will go wrong.” Gaster closed both eye sockets and ran his hand over the crack above his right eye socket. 

“As cliché as it sounds, the day began like any other day.”  
…………………………………………………………………………………………………………………………………………………….  
Gaster was tapping his foot impatiently as he glared at the digital watch on his wrist. Alphys was late. This was a bad habit she was getting into. For the past few weeks, she has come running in five or even ten minutes late claiming that her animes had run long. Was that what they were called? animes? Ani-nay-nays? Animies? Whatever, the point was that they were just flashy cartoons. He didn’t understand why she didn’t just pause the show until she was done with work. 

After ten minutes had passed Gaster threw up his arms in frustration. “Oh don’t worry Alphys, we’re just working on groundbreaking research that could be vital to monsterkind’s survival. No need to be punctual or anything silly like that,” Gaster raged sarcastically to himself. 

It was time to stop fooling around. He had work to do and he was prepared to do it with or without Alphys. 

Gaster looked down at his clipboard and began marking things off the checklist. 

The DT Gun was prepped and ready to go. Test subject 37, a dog monster from the Greater Dog Tribe, was strapped to the examination table situated directly below the DT Gun. Gaster did not have high hopes for this test. Greater Dogs tend to have higher concentrations of magic that enable them to slip into armor up to five times their size and control it like an actual extension of their physical body.

DT and magic don’t mix. Chances are this was just another failed experiment in the making, but he had to try anyway. 

Gaster flipped a switch that turned on the laser guidance system. He watched the screen which was mounted just above the control panel. A red dot appeared on the canine’s bright white fur and moved until it was properly stationed over the monster’s chest where the soul was housed. Gaster’s hand was poised above a large red button waiting for the green light to signal. It wasn’t long before the green light on the control panel flashed and Gaster pushed down on the red button that would fire the DT injector. 

But nothing happened.

Gaster pressed the button again but still nothing happened. He watched as the red dot on the dog monster flickered and died. The DT Gun was malfunctioning!

“Damn!” Gaster slammed his fist against the control panel. 

That was a mistake. The screen above the control panel faded to black and now he had lost visual! Punching the control panel like the impulsive moronic fool that he was, must have jostled a loose wire causing the monitor to lose connection.

“Double damn!” 

Gaster set down the clipboard and grabbed a toolkit from the closet before running out the door. 

He could worry about the monitor later. Technically he could still perform the experiment without visual as long as the laser guidance system was still workings. He and Alphys had performed a few DT tests with the DT Gun before he installed the cameras and it worked just fine.

Standing at the door of the DT examination room, Gaster pressed his hand against the hand scanner. A white light flashed across the scanner as it read his unique hand signature. After the scan was complete the scanner buzzed in acknowledgment of Gaster’s authority and the doors hissed open. Heavy security was necessary for obvious reasons. Even though only he, Alphys, and Asgore knew of the hidden lab that resided below the other lab, he didn’t want to take any chances. 

Angrily striding across the room, Gaster unceremoniously shoved the steel examination table the Greater Dog was strapped to out of away. The table rolled until it bumped harshly against the wall. 

The Royal Scientist was not in a good mood. First Alphys failed to show up, and now his equipment was breaking. Gaster pulled a panel off the machine. He knew a bit about mechanical engineering, but this was definitely something he really would have preferred Alphys to handle. Why couldn’t she be more punctual? 

He knew the DT tests were putting a strain on her but this was important work. Gaster’s brow furrowed in irritation. If she ever wanted to succeed him, she was going to have to start putting aside her personal feelings on difficult subjects. Avoiding work by sitting at home and watching cartoons was something a royal scientist wouldn’t be allowed to do.  
Gaster shined a flashlight into the machine and saw the various jumbled cables and wires. This was a mess. There were wires crossing every which way and nothing was tagged or labeled in any kind of way that would have helped him navigate this bird nest of tangled wires. Now he really wished Alphys were here.

He stuck the butt of the flashlight into his mouth so both hands were free to pull apart the mess of wires. With his focus completely consumed by the machine in front of him, the scientist failed to notice that a tiny dot of red light had flickered into existence above his right eye socket. 

Gaster tugged at an orange wire. He had no clue what it did, but it was tangled up good. He was about to summon a pair of magic hands to assist him but froze when he heard a whirling noise coming from somewhere deep in the machine. What the hell is tha-

-BANG!-

“Araahh!”

There was an awful crunching sound and pain erupted across his skull as bone fragments flew in every direction. The flashlight dropped from Gaster’s mouth and he stumbled backward. His eye sockets widened and his pupils shrank in shock. 

He could feel hot liquid pouring into his skull. “N-no! Wh-wha… what!?” he cried in confusion. 

Gaster fell to his knees. With a shaky hand he reached up and felt an object protruding from his skull.  
It was the injector. He had been struck by the DT Gun.

The injector was essentially a heavy-duty syringe designed to pierce through the chest cavity of the toughest monsters so that it could reach their souls. And… and now it was i-in his skull? That means the liquid he felt. It was… it was DT! He had to get it out! He had to get it out right now! 

Gaster gripped the injector tightly in his skeletal hand. He closed both eye sockets and his breathing became erratic as he braced himself for what was to come next. 

He jerked it upward as hard and as fast as he could.

“RRRAAAHHH!” 

Gaster roared as the long, thick, steel needle was slowly pulled up and out of his skull. It hurt significantly worse coming out than it did going in. 

When he finally managed to pull it free, his arms dropped to his sides and the injector rolled out of his hand. He took a few unsteady gasps of air. 

That was bad… but he needed to see… he needed to l-look. Slowly he looked down at the injector and his worse fears were confirmed. The glass casing that held the liquid Determination was empty. He tore his eyes way from the empty injector and looked down at himself. His White turtleneck sweater was stained black. Black like DT. 

Gaster understood what was happening. The DT that had been injected into his skull was dripping out, cascading down his bones, and flowing directly into his chest cavity. DT was oozing directly onto his soul! He was about to pull off his jacket and sweater when every bone in his body suddenly throbbed in pain.

“No!” he cried weakly as he stiffened and fell to his side. His bones felt like they were on fire! Was he melting? It usually took a day or two for the other test subjects to melt, but Gaster could clearly see his bones starting to liquefy already. No! NO! He couldn’t die like this! Not like this! Gaster screamed in agony but he couldn’t hear anything. It was silent, his screams were completely silent. 

As he writhed on the ground he thought of all the things he still had yet to complete. He still needed to find a cure for the illness or find a way to destroy the barrier. He still needed to fix the Chrono Chamber that held the waste particles that were being expelled from the Core. And lastly, he still needed to develop a weapon powerful enough to eradicate every last human from the surface world. 

These were his goals. 

Alphys was smart but she didn’t have the drive to find a cure or find a way to destroy the barrier without his help. She might be able to fix the Chrono Chamber, but would she be able to do it in time before a leak occurred? And he knew Alphys was too soft to even consider designing a weapon capable of eliminating the human threat.

He had to live. He needed to live. He was determined to live! 

Dark purple light burst from between his ribs. 

The last thing he saw before passing out was the door opening and a hysterical Alphys running in shouting, “Oh my God! Doctor Gaster, I’m sorry I-I’m s-so sorry!”  
…………………………………………………………………………………………………………………………………………………….  
Sans was silent. 

Gaster knew Sans was processing all this information. It was a lot to take in. He had told Sans everything. Everything except about the incomplete goals he was thinking about as he lay on the examination room floor. Sans already knew about his first goal to find a cure for the illness or find some way to break the barrier, but it wasn’t necessary for Sans to know about his other personal goals. At least not yet.

“A week later I woke up in the hospital. Alphys was there and she told me that when she came in that morning she had found the clipboard that I had left on the control panel. It wasn’t unusual for me to leave instructions for Alphys on a clipboard whenever I left the room and she just assumed the contents of the clipboard was something she was supposed to follow. She knew as well as I did that she could perform the test without having a visual of the actual exam room. Even though the machine malfunctioned for me it, unfortunately, worked just fine for her.”

Gaster had a hurt look on his face as he whispered, “It was my entirely my fault. I even told her so, but she was never the same after that. She… She was so confident and strong, but seeing me injured on the exam room floor broke her somehow and she lost her confidence!” Gaster was getting angry but he was only angry at himself. “After I had healed and returned to the lab, Alphys began making stupid mistakes. Her lack of self-confidence was sabotaging her work and not long after that she stepped down from her position and transferred over to the engineering division.”

Gaster’s eyes meet Sans’. “And that’s when you were hired,” he said simply. 

“what about the DT experiments?” Sans asked. 

“Asgore visited me while I was in the hospital and told me that effective immediately we could no longer experiment on other monsters using DT.” Gaster smirked and added, “But he didn’t say I couldn’t experiment on myself.”

Sans looked outraged. 

Gaster held up a hand and said, “I know it sounds bad, but after what happened in the DT examination room, I began to notice I was getting stronger.” He shivered and whispered, “A lot stronger. My magic and physical strength have skyrocketed since then, and now I take DT tablets to continue to gather my strength. It’s only been recently that I’ve noticed… a _side effect_.”

Gaster told Sans about how he would black out and miraculously find objectives he had been determined to finish completely finished for him. 

“It wasn’t harming anyone and I sincerely thought it was a good thing… until last night.” 

As soon as Gaster was finished telling Sans about his encounter with his determined self in the mirror, he observed that Sans had gone pale and was starting to perspire. The smaller skeleton then sat up straighter and said, “you… you wanted to do that to me? you were determined to violate me like that?” Sans couldn’t keep the rage he felt out of his voice. 

The silence that followed only made him angrier. “answer me!” he demand. 

Gaster cringed and shouted back, “I don’t know how to answer that Sans! I know for a fact that did not want that consciously, but I wouldn’t rule out the possibility that the DT might also be latching on to primal urges or intrusive thoughts!” He knew the DT had focused in on his desire for Sans, but what it truly attached itself to was a fleeting inappropriate thought about how he wanted to dominate his young assistant. He was embarrassed and disgusted with himself.

“what’s that supposed to mean?” Sans grumbled. 

“Have you ever had a thought cross your mind about wanting to do something that was so unbelievably heinous even you were disgusted by it? For example, let’s say you and a friend are standing at the top of a cliff and for some reason you think about what would happen if you shoved your friend off. Obviously you would never do that, but the urge to do so was there nonetheless!” 

Sans sagged. Yes, he has had thoughts like those before. One time he had even thought about punching Papyrus in his cute, smiling face for no reason at all. He felt awful just thinking about it.

Gaster saw the look of horror flash across Sans’ face. “doc, if it’s true that the DT is latching onto those kinds of thoughts then you need to stop taking that shit right now!” 

The older skeleton nodded and said, “Yes, I believe once I stop taking the drug my determination will fade.” They both sat in silence once more. 

Sans had just a few more questions. He looked up at Gaster and said, “you said your determined self had been plotting this thing for over a month right? well, how did he know i would volunteer to be your test subject?” 

"Good question. I do not believe it knew you were going to offer yourself up to be my test subject, but I do believe it knew you wouldn’t pass up an opportunity to fix your hp related sleeping problem.”

Sans accepted that answer and said, “i have another question.”

“Go ahead, Sans.”

“if your determined self was able to show you the memories you were missing from your blackouts, then why did it find it necessary to use a video camera?” 

At first, Gaster didn’t know how to answer that, but then it dawned on him. “I… I think it was purely a tool used to control you.” Gaster felt vaguely sick but continued, “I threatened to blackmail you, correct? The threat kept you from fighting me a much as you would have otherwise.” 

Gaster looking pale and defeated, whispered, “I’m sorry Sans. I’m so sorry I did this to you.”

Sans clenched the blankets resting in his lap. He hated it. He hated what the DT had forced Gaster to do to him. After a few minutes of debate, he looked at Gaster and said, “you didn’t do it on purpose.” 

“What?” Perhaps he hadn’t heard Sans correctly.

“you didn’t do it on purpose, so i forgive you.” Sans shrugged. He didn’t want to say it wasn’t his fault because he felt it was still a little bit Gaster’s fault, but he was able to come to terms with the fact that Gaster didn’t do what he did on purpose. 

Gaster’s expression was unreadable. Slowly he said, “Thank you, Sans, I don’t deserve your forgiveness, but thank you.” 

Sans rubbed the side of his skull and groaned. “this is a lot of information to digest, but since i know all this information, what are we going to do now?” 

“Well…” Gaster chuckled darkly and his eyes turned purple. “I suppose now I can erase your _memory_.”

**Notes for the Chapter:**

> Uh oh. Hahahaha!


	10. Dangerous

The room was dead silent as Sans stared at the man sitting across from him. Gaster’s eyes were purple, but they weren’t _dark_ purple. Slowly an unsteady grin spread across Sans’ face and the lights in his eye sockets vanished. Keeping his voice as level as possible Sans said, “this is a joke right? cuz i can tell you’re uh… not very _determined_ right now are ya, doc?” Gaster smirked and slowly rose from his seat. “How very observant of you Sans. Yes, you are correct, I am not determined right now but I _am_ being completely serious.” 

Gaster flexed his right hand and sighed dramatically. “You know what’s ironic Sans? Being a master of mind magic and realizing that you’re gradually losing your own mind.” He could practically feel the madness that was DT pounding at the doors of his mind. If he was going insane… if he was becoming dangerous… then he wasn’t about to bring Sans down with him. Even if he stops taking the DT it could be a while before all of the drug has depleted from his body. He couldn’t risk Sans being close to him while he still had so much DT in his system. 

He couldn’t trust Sans to stay away from him on his own. His loyalty, while admirable, could potentially be detrimental. There was only one way to protect his assistant now.

Sans tried jumping off the bed and running for the door, but Gaster was incredibly agile. The taller skeleton grabbed Sans around the middle before he could run past him and slammed him back onto the bed. 

“I can promise you that this will be painless as long as you stop struggling,” Gaster grounded out through clenched teeth. Sans thrashing and kicking against him was _really_ starting to annoy him.

Sans’ left eye flared to life. Trying to be clever, he summoned a bone behind the unhinged scientist and fired. 

The bone sped straight towards the taller skeleton’s unprotected backside. 

Without breaking eye contact with Sans, Gaster snapped his right arm back behind himself and snatched the bone right out of the air before it could make contact. He then brought it close to Sans’ face before breaking it into two with his fist. It was clear the powerful scientist was done playing games. 

Holy shit! He was so _boned_. Sans thought as he watched the useless pieces of his bone attack fall from Gaster’s hand. Fear overwhelmed him and he started to tremble. Gaster now had both of Sans’ wrists pinned above his head with his left hand. His right hand erupted into purple flames as he brought it towards Sans’ temple. 

He was about to perform the mind wipe when he felt Sans trembling beneath his grasp. 

Pulling back slightly, Gaster could see the fear and betrayal in Sans’ eyes. 

Seeing all that fear caused Gaster to pause and question his actions. This was for Sans’ own good, wasn’t it? He could protect Sans better if the younger skeleton didn’t remember what happened last night and had no knowledge of DT. He hated what he was doing but he couldn’t stop.

Looking down at the frightened skeleton beneath him, Gaster hummed in thought before saying, “You’re not going to remember this anyway, but for what it’s worth, I really do care about you, Sans.” With that Gaster had his mouth pressed against Sans’ in a gentle kiss. 

Sans stopped trembling and went rigid in shock as Gaster’s mouth pressed against his own. His rage swirled and bubbled at the other skeleton’s audacity. He was about to headbutt the bastard in anger when he felt something warm and wet splattering against his face. Looking up in confusion, Sans could see Gaster’s eye sockets were shut tightly but a steady trail of tears were dripping down his face.

Crying. Gaster was crying. 

The hand clutching Sans’ wrists slackened slightly. 

Now was his chance!

Sans ripped his left arm out Gaster’s grasp and then thrust the palm of his hand against Gaster’s exposed ribs. The taller skeleton gasped as his soul went from purple to blue instantaneously. Sans then flicked his wrist and Gaster was launched skyward until he crashed into the ceiling. His glasses flew off his face and landed on the carpet below. Keeping his left arm extended and pointed directly at the other skeleton, Sans shuffled off bed holding the long black lab coat tightly around himself. 

He walked over to the fallen glasses and plucked them off the ground. Staring up at the skeleton plastered against the ceiling, Sans grinned and twirled the glasses around his finger. “wow doc, first the antigravity belt and now this? you and the ceiling must have a real _attachment_.” He then shoved the glasses into the front pocket of the lab coat. 

Gaster didn’t say anything but if looks could kill then Sans would have been dust ten times over. 

Gaster was silently berating himself for losing control of his emotions and allowing Sans to get the upper hand. This whole DT situation has become a major stress factor in his life and it was clearly wreaking havoc on his emotional wellbeing. He should have just erased Sans memory while he had the chance instead of getting foolishly sentimental. He could see now it had been a mistake to become emotionally invested in his assistant. It was… making things difficult.

“i thought after i forgave you we could’ve moved on, but apparently something is still very wrong.” Sans’ grin became strained and he said, “perhaps you could tell me why you’re trying to zap my mind right after the nice long chat we just had.”

Gaster smiled but it didn’t quite reach his eyes. “Hmm… you appear to be under the illusion that you have some kind of authority over me just because you have me pinned with your magic. Don’t be stupid Sans, I think you know as well as I do that I can still easily destroy you even in my current predicament.”

Three bones materialized in front of Gaster and aimed themselves at Sans.

“Release me Sans. NOW!”

“no.”

Gaster’s pupils constricted. “What!? You insolent little-”

“i’m not going to release you, and i don’t think you’d ever intentionally hurt me. i mean, you did just say you cared about me right? so why don’t you cut the bull crap and tell me why you feel the need to erase my memory.” Sans sounded confident but he was shaking slightly. He sincerely hoped his assumptions about Gaster were right or this was going to end very badly.

“You still won’t release me? So be it.” Gaster snapped his fingers and the summoned bones shot at small skeleton on the ground. Sans clenched his eye sockets shut tightly. There were three loud thudding noises and then there was silence. 

…

Well, he didn’t _feel_ dead, so he supposed that was a good sign. Sans opened his eye sockets and looked around. Three large bones were embedded in the ground around where he was standing but none had even come close to hitting him. He then looked up at Gaster and smiled victoriously.

Damn! Gaster was incredibly frustrated that Sans was able to call his bluff so easily! He was completely correct. He wasn’t going to hurt him. The whole point of erasing his memory was to protect him! He was just hoping he’d be able to frighten Sans into releasing him from this blue magic trap.

Gaster dispelled the bones. “Don’t look so smug Sans, my glasses fell off. Obviously, I just couldn’t see my target properly,” he muttered. 

Sans winked, “heh sure, whatever you say doc. now i really gotta know, why would you waste time telling me everything if you were just going to erase it from my mind anyway?”

“Ah well, I suppose I just had a lot of things I needed to get off my chest. So thank you, Sans, for letting me use you to vent my frustrations, but now I really must insist you release me so I may finish this.” Gaster smiled but it was crooked and twitchy. 

“you’re such liar.”

Gaster raised a brow. “Pardon?”

“i said you’re such a liar! it’s written all over your face!”

“Don’t pretend like you know me at all,” Gaster growled. 

“stop it!” Sans cried. He pulled Gaster about a foot away from the ceiling before slamming him back against it causing the older skeleton to grunt in pain. It didn’t really hurt, but it sure didn’t feel great either. “just… stop.” Sans was getting tired. He couldn’t hold Gaster with his magic like this for much longer, it was exhausting him.

“i… i don’t want to forget everything that’s happened, gaster,” Sans said quietly. He ran the hand that wasn’t pointed at Gaster down his tired face. “please don’t make me forget.”

“T-that’s what Alphys said too,” Gaster relented.

“huh?” Sans looked up at Gaster and noticed the taller skeleton had stopped struggling against his blue magic and was now limp with an expression of sheer defeat of his face.

“I offered to erase the memory of the DT accident from her mind so it wouldn’t burden her anymore, but she refused. I respected her decision but now I wish I had just gone ahead and erased her memory anyway. Sh-she was like a daughter to me and now she can’t even look me in the eyes! Do you know how much that hurts?”

“n-no,” Sans stammered and shook his head.

“That’s right, you don’t! And now the DT has hurt you and it potentially could hurt you again! I wanted to erase this whole night from your memory so I could protect you. So I could remove you from myself without you being a stubborn little shit with a misplaced sense of devotion! I knew that if you stayed by my side you could get killed or… or you would get hurt again and leave me. Dammit Sans, I’ve already lost one assistant I cared about, I don’t want to lose another one, alright?” Gaster looked like he was in the midst of a panic attack. His breathing had become haywire and he only seemed to be able to take in small gasps of air. 

“that’s what this was all about? you’re afraid you’re going to hurt me or do something that will cause you to lose me? But wouldn’t erasing my memory and pushing me away be losing me too?”

Gaster was still trying to get his breathing under control but he managed to choke out, “I’d rather…” Gaster took a ragged breath of air. “... have you at a distance and be safe than have you close and possibly come to harm.” His breathing was getting worse. Damn! He needed to get to his nightstand. He needed to get his…

“S-san!” Gaster wheezed in panic. “I c-can’t breathe!”

It took a moment for Sans to realize what was happening, but when he did he shouted, “oh... oh man! hold on doc!” Sans lowered the gasping scientist to the floor and ran over to him. 

“where is it? where is your-“

Gaster pointed to the nightstand. Sans ran over to it and yanked open the drawer. After shoving the tape recorder and a bunch of other junk aside, he found what he was looking for. He grabbed the small red tube and ran back.

“i’ve got it! i’ve got your inhaler.” Sans shook the red tube before pressing it to Gaster’s mouth. Gaster reached up and grabbed a fistful of the black lab coat draped around Sans in desperation.

Sans pressed the top of the inhaler releasing the gas.

-Kisssssst-

The change in Gaster’s breathing was instantaneous the moment he breathed in the lifesaving gas. His breathing evened out and he was no longer struggling to draw in air. With his breathing back to normal he rested the back of his head against the floor and exhaled in relief. Sans looked down at the taller skeleton and said, “sheesh doc, i know i’m breathtaking but that was a bit ridiculous.” Sans laughed as Gaster groaned at his crummy joke. 

The scientist then turned to his assistant and whispered, “Thank you, Sans.” Even after everything he’s put Sans through tonight, Sans still assisted him without hesitation when he needed it. Maybe he had been wrong. Maybe Sans wouldn’t abandon him like Alphys did. However, that didn’t change the fact that his DT fueled self could still reemerge and harm Sans again. Was he really willing to risk his assistant’s life by keeping him close instead of pushing him away?

Smiling Sans said, “heh, no problemo, my little bro had asthma when he was younger, but thankfully he grew out of it.” Most people would think skeletons wouldn’t get asthma because they don’t have lungs, but the reality of the situation was that skeletons breathe using magic to draw air in and out. Unfortunately, like regular lungs, magic ‘lungs’ can get messed up sometimes and require medication. “why didn’t you tell me you had asthma?” he asked.

Gaster looked away from Sans. “It usually only acts up when I get in a dither. I didn’t use to need and inhaler. It was only after I got injured that I started needing to use one.” Gaster pressed a hand to his cracked ribcage.

“did your ribs get injured during the DT accident too? Sans asked. He reached down and touched one of the cracks on Gaster’s ribs with the tip of his finger. The older skeleton flinched away from Sans’ touch causing Sans to withdraw his hand. “sorry.”

“N-no it’s… it’s okay,” Gaster said quickly, realizing his mistake. He reached up and wrapped his hand around Sans’ and brought it back to his ribcage. A small blue blush crept across the younger skeleton’s face as Gaster held his hand firmly against his ribcage. He could feel the powerful skeleton’s soul pulsating through the ribcage beneath his hand.

“My ribs weren’t injured during the DT accident, but I think I’ve told enough stories for one day don’t you think?” Gaster released Sans’ hand and looked up at him in silent contemplation. 

After a few long minutes of ferocious internal debate, Gaster finally said softly, “I’ve been such a fool, haven’t I?” 

Sans wasn’t looking at Gaster. Instead, he was focused on tracing one of the long cracks on the other skeleton’s ribcage with his finger. “yeah, i reckon you have been.” Gaster couldn’t help but exhale deeply at the pleasant sensation of Sans’ gentle touches.

“You need to know that I can’t ensure your safety if you still desire to stay by my side.”

“ok.”

“Until the DT wears off I could become determined at any point in time.”

“ok.”

“I could hurt you again, or even kill you.”

“ok.”

“I could erase your memories of this night and we could go on as if none of this has ever happened. You won’t be burdened by what you’ve learned here. Or… or I could even erase all your memories of me entirely and have you transferred to a different science division. It would be the safest place for you. I could keep tabs on you without you being in the direct line of fire.”

“you know that’s not what i want,” Sans said simply.

Gaster nodded and said, “Yes, I know. I thought I should offer you that option anyway just to make sure.” 

Gaster then raised his hand to Sans’ face and gently grasped his chin. He applied just enough pressure to force Sans to turn and look at him. “I’m not a good monster Sans, I’ve done a lot of awful things that I’m not proud of, but at the same time, I’ve done a lot of awful things I don’t regret either.” 

Sans looked him directly in the eyes and said, “doc, i don’t think you’re a bad monster. i think you’re an impulsive idiot who’s had a shit load of problems unfairly dumped on him. i think the pressure of everything that you’ve been asked to do for monsterkind has made you take desperate measures as a means to keep up with the unfair demands being hurled your way. and lastly, i think that you need someone to help keep you grounded as you attempt to fulfill these demands.”

Sans then stood up stuck out his hand towards Gaster. “so please sir, let me help you.” He was echoing his words from a few weeks ago when he had asked Gaster to let him help him on his personal science experiments. It seemed so long ago now.

Gaster stood up too and without any hesitation, he grasped Sans’ hand with his own and said, “Let’s do this together then, Sans.” The younger skeleton flashed him a genuine smile that caused Gaster’s soul to vibrate in his chest.

Just as Sans was about to pull away from their handshake, Gaster gripped the small hand a bit tighter and jerked him towards himself. The small skeleton let out a gasp of surprise as he was pulled roughly against Gaster’s chest. 

Smirking as he watched a bright blue blush spread across his assistant’s face, the scientist reached down into the front pocket of his own lab coat that was currently being worn by Sans and snatched his glasses. This was an all too familiar situation. 

Placing them back on his face he chuckled and said, “I must once again thank you for keeping these safe for me.” This time instead of releasing the smaller skeleton, Gaster drew Sans closer to himself and pressed a delicate kiss to his mouth. Their teeth clacked gently together and Sans could feel himself getting weak in the knees. Despite everything that’s happened tonight, this right here felt incredibly _right_. 

Gaster suddenly shivered and abruptly pushed Sans away. Laughing nervously the older skeleton rubbed the back of his skull and said, “Uh, Sans? I think perhaps you should go put some clothes on.” 

Looking down at himself Sans let out an undignified squeak and pulled the black lab coat tighter around himself. He had completely forgotten that he was naked under the coat! Grabbing the neatly folded clothes off the nightstand, he fled towards the bathroom.

“Watch out for the broken glass!” Gaster called as Sans slammed the door shut. Still laughing Gaster pulled out a new, slightly beige, turtleneck sweater out of his dresser and pulled it over his head. It wasn’t as good as his old turtleneck, but it will do. 

He was sitting at his computer when Sans finally walk out of the bathroom now fully clothed and bandage free. “hey doc?”

“Wingdings.”

“huh?”

“I think we are familiar enough now with each other that when we’re not at work you can call me by my first name.”

A huge cheeky grin spread across Sans’ face and he said, “sounds good to me, _dings_.” 

Gaster’s face instantly scrunched up in distaste at the nickname. “Ugh. Sans, no!”

Sans just laughed and said, “sans, yes!” He then shrugged and said, “what? would you rather me call you g?” When Gaster thought about it, he would much rather have his first name shortened to Dings than have his last name shortened to just the first letter. 

“Didn’t you need something Sans?” Gaster reminded the snickering skeleton.

“oh yeah! uh, what time is it?” Sans asked.

Gaster looked down at his digital watch and said, “7:45am” 

Sans’ eye sockets widened comically. “oh crap! we need to be at the lab like right freaking now!” 

Gaster watched in amusement as Sans ran around the room trying to tie his shoes and his necktie at the same time. 

Finally having pity on the panicked skeleton, Gaster said, “It’s Saturday Sans, the lab is closed.”

Sans paused and sighed in relief but then gasped. “papyrus! he’s going to be so pissed i’ve been gone for so long without checking in on him. ugh, i’m gonna have to read him like five bedtime stories tonight to make up for this!”

“Before you go I have something I need to discuss with you.” 

Sans swallowed thickly at serious expression on Gaster’s face and said, “uh ok, what is it?”

“Last night was… intense to say the least. I broke a lot of rules, and I even broke a royal promise by telling you about the falling down illness and DT.” Gaster rubbed the crack above his right eye in agitation. He then grimaced and said, “I’m going to have to tell Asgore what happened.” 

“what!?” Completely mortified Sans shouted. “n-no way! i do not want the king to know what happened between the two of us!” Having King Fluffybuns know what they did was the last thing he would ever want. 

“When I go to have my chat with him I promise I won’t go into detail about what happened, but I do need to tell him you know about the falling down illness and the DT experiments. I doubt he will be pleased, but I think I can convince him you will be a valuable asset in our search for a cure to the illness.”

Gaster then smiled at Sans and said, “I _do_ believe you will be a valuable asset Sans.” 

The smaller skeleton flushed a little and nodded his head slowly.

Gaster then stood up out of his computer chair and walked over to the door. “I’ll see you Monday, alright Sans?” He pulled the door open, and as Sans walked past him he winked up at him and said, “you got it, dings.” 

The moment the door closed, Gaster went back to his computer desk and pulled out the video camera from one of the drawers. He watched the video of him… _defiling_ Sans over and over again. Each time he watched it he felt like throwing the camera against the wall in anger. But he couldn’t. He knew he had to study the footage in an effort to gain as much knowledge about how the DT was affecting him as he could.

After the fifth time he watched it he couldn’t stomach it any longer. He shoved the camera back into the drawer and looked at the clipboard. At first, it seemed normal. Written on the clipboard was the data he had collected while observing the effects of the skeleton heat drug on Sans. However, when he flipped to the next page the only thing written was the phrase, HELP ME. It was written all over the page. His summoned magic hands had written that after the DT had taken over. How strange. 

Gaster rubbed his eye sockets with his hand in frustration. He then opened a different drawer and pulled out a container. He unscrewed the lid and tapped the container until a small black tablet fell into the palm of his hand. He held it up to the light and stared at its tiny shape. It’s amazing how something so small could cause him so much trouble. 

Something inside him throbbed with a powerful desire to consume the tablet. 

Growling, he quickly dropped the pill back into the container and tossed it into the drawer. He then extracted a different container and tapped it until several pills fell out. He shoveled those into his mouth and swallowed. 

_Painkillers_. He took a few more than was strictly necessary but damn did his head hurt. He sighed and leaned back in his computer chair and stared at the ceiling. He was NOT looking forward to meeting with Asgore. Asgore might be his oldest and dearest friend, but he was a very vexing individual at times. That bastard always liked to drag up the past much to his own displeasure. 

Right now he needed to sleep but he was afraid… afraid of the darkness. Afraid of the voice he had heard on the phone in his dreams. The voice of someone long dead. Gaster shivered and then grinned manically. Ha! What was he thinking? Of course he didn’t need sleep! He was the Royal fucking Scientist! He could concoct a new drug that could help him stave off sleep! Yes, that’s a brilliant idea. 

He grabbed the container of pills off the desk and shook it. Hmm… he was going to need _a lot_ more painkillers

**Notes for the Chapter:**

> Uh... I guess you can consider this end of Act 1. 
> 
> I found it pretty funny reading the comments on the last chapter. You guys all thought Gaster had become determined when in reality he was just being a spazy asshole! Oh, and yeah Sans doesn't have his shortcut ability... yet. 
> 
> I can't wait to write Asgore's part. I think you guys will find him very... _interesting_. heh.
> 
> Also, 8200+ hits on this story!?! Jeez y'all are thirsty for some Sanster. Just wanted to say thanks guys! your feedback gives me life! :D


	11. Everything is Fine

12:00AM

His face was basked in the red glow of the digital alarm clock sitting on a stack of cardboard boxes beside his bed.

It has been exactly 97 years, 4 months, and 24 days since the last human soul was gathered by the King. 

Yeesh, was he going to become as obsessive as Gaster about this whole lack of human souls thing? Sans rolled onto his other side and stared at the blank, white wall beside him. Here he was just lying on his bed trying to sleep, only to find that the immense amount of information running through his skull has made sleep nearly impossible. And that was really saying something considering he was, as Papyrus calls him, the Mayor of Snoozeville. 

He supposed that knowing his species was dying due to a bizarre sickness that’s akin to depression on steroids wasn’t exactly the kind of information that brings one peace of mind. Ever since he arrived back home to his crummy little apartment he shared with his bro, he’s been thinking nonstop about everything Gaster had told him. And you know what? As bleak as the future of his people looked, Sans couldn’t help but feel slightly relieved about one thing in particular. 

If the sickness stemmed from losing hope, then that meant his brother wasn’t in any danger of falling down. His bro was easily the most optimistic monster he has ever encountered. Out of all the monsters in the Underground, Papyrus was probably the least likely to be struck with the falling down illness. 

Sans looked over his shoulder at the lanky skeleton monster snoring in the bed on the other side of the cramped room. Even if his brother wasn’t likely to contract the illness, he was convinced that he needed to get the two of them out of the Capital as soon as possible. 

The Capital has become far too overcrowded and the atmosphere in the city was so tense it was suffocating. It wasn’t an environment that would allow Papyrus to flourish, and he’s known that for a while now. The place was so stagnant. He didn’t want the bleak humdrum of city life to rub off on his brother, or on him for that matter now that he knew the triggers for the illness. 

Maybe that’s why Gaster lived in Snowdin. Maybe the good doctor left the city when he found out it was literally sucking the life out of everyone. Or maybe he just didn’t want to be reminded of the fact that the fate of all these monsters rested almost entirely on him and his ability to find a solution to the illness. 

Gaster, he… uh, he was really somethin’ else. There was no denying that the man had issues. _Serious issues_. And not all related to DT either, but who could blame him? No one single individual should have that much pressure bestowed upon them.

Not only was Gaster in charge of finding a cure for this illness, he also ran a top-notch laboratory, assisted other scientists with their projects, developed his own projects, runs multiple experiments that often requires him to stay at the lab for days on end, and he’s the official liaison between the Royal Bureau of Science and the King. On top of all that, Gaster had developed, built, and now maintains the Core. The Core powers everything in the Underground. Without it, we would all be huddled around campfires just trying to stay alive. 

Yes. Without a doubt, Dr. Gaster was an amazing monster. 

He was also an asshole. 

Like holy crap, a seriously inconsiderate asshole. 

Sans still couldn’t believe that the bonehead had actually tried to erase his memories without any kind of consent from himself. What the hell was his major malfunction? Sans wasn’t an idiot, he knew DT couldn’t be blamed for all of Gaster’s odd behaviors.

Sans drew his sheets up closer around himself. 

Gaster wasn’t a saint that’s for sure. He has experimented on, and even killed monsters. Sans was still alarmed and disgusted by Gaster’s actions. He was also beginning to think that Gaster might not even view the destruction of the melted monsters as a bad thing. Gaster had claimed that everything he has done has been _for the greater good_. The man himself was practically the embodiment of some twisted form of utilitarianism. 

Gaster sacrificing the few for the good of the many was just one example. Heck, Gaster basically sacrificed himself on a daily bases for the good of monsterkind. He was essentially obsessed with saving the monsters that dwelled in the Underground, and maybe the old skeleton is right to be obsessed. Monsterkind was in dire need of saving and someone has to at least try and save us, right? 

Except… except it was _killing him_! It didn’t take a genius to figure out that Gaster was teetering dangerously close to an edge that could only lead to self-destruction. Sans could understand sacrificing yourself for the good of others, but the way Gaster went about it was needlessly risky. It was like the man had a death wish or something.

Sans grounded his teeth together in irritation, which sounded as unpleasant as it felt. 

“Saaanss, don’t dooo that...” Papyrus whined, though still very much asleep. Sans whispered back, “sorry bro,” but Papyrus had already gone back to snoring.

Just thinking about the reckless older skeleton frustrated him deeply. 

But then, if Gaster causes him so much grief, why does he keep risking his own life by volunteering to help him? Was it out of pity? He definitely felt the universe has been particularly unkind to the Royal Scientist, but so what? The universe has been unkind to him and his bro too. 

Okay, so then maybe it was empathy rather than pity. Except, that still doesn’t explain why his soul does flip-flops every time the man so much as smiles at him. Sans had thought it was just a small crush, but when Gaster had kissed him, like _actually_ kissed him the other day just before he left, it felt like his whole world had gotten just a little bit brighter. 

If this wasn’t just some silly crush, then what was it?

Sans smiled lazily and the tips of his fingers brushed his mouth as he thought about the kiss. Pfftt… he was such a sap he should’ve been born a freakin’ tree. 

Maybe he was a little crazy too. Any sane monster would have fled as soon as possible after everything that happened while Gaster was under the influence of DT. He on the other hand just stuck out his hand and told Gaster he wasn’t going anywhere. That he was going to stay by his side despite the obvious dangers and help him. 

_‘I could hurt you again, or even kill you.’_

Sans stiffened as Gaster’s words resonated in is mind. Tsk, he always talked about what a reckless idiot Gaster was, but maybe he was a hypocrite because it had definitely been reckless and idiotic of him to have just looked past the fact that Gaster could very well endanger his life again. What would happen if Gaster’s Determination surfaces again and the man ended up killing him? What would happen to Papyrus? 

Sans rolled over again so he could look at his brother. His bro was so innocent and too trusting for his own good. Who would help him navigate through this unforgiving world if he wasn’t there to help guide him? They had no friends, no family. They only looked after each other, and that’s the way it’s been for a very long time. 

At least it wasn’t as bad as used to be. They might only have each other, but at least now they have an actual roof over their heads. He and Papyrus would probably still be living on the streets if he hadn’t received Asgore’s Royal Scholarship that enabled him to attend the local university. 

With that scholarship, he was able to receive a decent education and land a great job that paid him just enough so he could afford the rent for this ultra shitty apartment. But hey, at least he no longer had to steal ketchup packets and water sausages from food vendors. He could buy him and his bro as much food as they wanted. That was a great feeling. 

So would Papy be back on the streets if he were to die? 

Sans grabbed a pillow and held it against his face as he groaned. The pillow muffled his groans so Papyrus couldn’t hear him. 

He did not want to think about Papyrus being alone in the world without him. He did not want to think about Gaster possibly hurting him again. He did not want to think about his confusing feelings for the Royal Scientist, and he did not want to think about the nearly inevitable extinction of his people. 

He was so tired. 

Sans pulled the pillow off his face and glared at the alarm clock. It was 12:15AM. Today was Sunday. It also happened to be the day Gaster goes to his monthly meeting with King Asgore. Today was the day Gaster was going to have to go before the King and admit that he had broken a royal promise. He was going to have to tell the King that his lab assistant was now fully aware of the nature of the falling down illness and DT. Would Gaster be punished for telling him? 

Gaster had seemed kind of apprehensive about telling the King about all this. But hey, anyone would be freaked out about giving the King bad news, even if the King was a huge fluffy pushover. Sans really hoped that when he got to work on Monday, Gaster will have nothing but good things to say about his meeting with the King. 

Sans suddenly sat up in his bed. 

Crap! He just now realized he had forgotten his lab coat at the lab. His lab coat had his security clearance badge clipped to it! Ugh. He was going to have to call someone to open the lab door for him Monday morning. That will just be a _brilliant_ start to his week. He slapped himself in the forehead and fell back onto the mattress. He recalled taking off his coat, but it had to be in the lab somewhere, right?

Sans had no way of knowing that Gaster had actually already disposed of his ruined coat. 

Staring up at the ceiling, Sans could feel himself starting to drift to sleep. It’s a good thing it was his day off today so he could sleep in as late as he wanted, or at least until Papyrus dragged his bony ass out of bed. 

Sans yawned.

Heh, he wondered if Gaster was currently sleeping with his thumb in his mouth like a total dork. And with that, Sans fell into a deep sleep whilst sporting an amused smile. 

…

Unfortunately Gaster wasn’t sleeping with his thumb jammed into his mouth. In fact, Gaster wasn’t sleeping at all. 

The Royal Scientist was currently pacing back and forth in front of his chemical mixer like a hungry, caged animal. He had been working all Saturday on a drug that would allow him to stay awake and alert for long periods of time. Nothing in the Underground came close to what he needed to stay awake, so he had to create his own stimulant. 

He wanted to play with methamphetamine, but unfortunately the Underground seriously lacked the substance. Monster’s typically had no need for such drugs. If they needed energy, monsters usually partook in some kind of caffeinated beverage and that was sufficient for them. But it wasn’t sufficient for _him_. Therefore, the first half of his Saturday had been spent rummaging through the garbage dump looking for any stimulants that had dropped from the human world.

He extracted what he needed from the drugs he managed to find and was currently trying to synthesize something he himself could use. 

It has been a little less than 24 hours since he last slept but he was tired from sifting through piles and piles of garbage at the dump. Most of the trash had come from the human world. They were such a wasteful species. 

At one point during his search, he had managed to dig up an old training dummy, which he then decided to punch at full force. It felt good. 

After he retrieved the discarded stimulants, he had returned to his home in Snowdin. Now he was currently in his own lab that was located in the basement of his home, staring at the chemical mixer. The mixer was exactly what it sounded like. It was a small machine that held tray full vials of chemicals and gently rocked back and forth effectively mixing the chemicals thoroughly. 

Gaster looked down at his watch. 

Unfortunately, the drug won’t be finished before he was required to join Asgore for his monthly meeting. Which was perfectly fine, because he’s stayed up far longer than this before. One time he had even stayed up three days straight because he had to fix an important part of the Core that had broken down. If he could stay awake for three whole days he should have no problem remaining awake and alert for Asgore. Of course, after those three days were up he crashed and burned hard. He ended up sleeping for a day and a half after that. 

He was hoping to avoid the crash in energy this time. As long as he takes the newly developed stimulant before a crash happens everything should be just fine… r-right? …right!?  


Gaster opened a drawer to grab something when his hand hit a small container. Confused, he extracted it out of the drawer. 

It was a bottle of DT. 

He had forgotten that he had stashed a bottle of DT down here. He… um, he should probably flush these down the sink or something. 

Gaster suddenly froze. He stared at the bottle for a few moments before placing the bottle full of DT back into the drawer and taking a step back. He was sweating bullets and rubbing the crack above his right eye compulsively. 

Everything is fine.

Everything is fine.

Everything is just _fine._

Gaster shook his head. He wasn’t feeling very well all of a sudden. He popped a painkiller into his mouth before ascending up the stairs so he could take a shower and eat something before his meeting with Asgore. 

Everything is fine.

**Notes for the Chapter:**

> DT, Sleep deprivation, painkillers, and stimulants. What could possibly go wrong~? 
> 
> As someone who has their degree and works in the field of psychology, I can assure you that everything. Everything can go wrong. Also for the record, Gaster doesn't have a firm grasp on pharmaceuticals. He thinks he knows what he's doing but he doesn't. 
> 
> Wow, I can't believe it's been a full month since the last update. Sorry about that guys! I wrote the last chapter in a single day and burnt myself out because I didn't want to take my time with it. I also had a serious case of writer's block. But now I'm baaaack! 
> 
> In this chapter I wanted to get a little more of Sans' thoughts on recent events. Poor kid, he's so conflicted. 
> 
> Next chapter we will get our first look at Asgore Dreemurr!


	12. Asgore Dreemurr

The Royal Scientist stood at the entrance to the Hall of Judgment. The hall itself was breathtakingly beautiful with its towering golden pillars that supported its high ceilings, and its excellently crafted golden stain glass windows that cast a dazzling pattern on the tiled flooring when the light from the outside hit them just right. 

He hated this place with every atom that constructed his being. 

This place was called the Hall of Judgment because it was the only area in the Underground where a monster can see another monster’s LV. Having one’s LV displayed then leaves the monster open to judgment from other monsters. The whole process was completely degrading. 

He had been born with an unusually high LV. Most monsters are born with an LV between 1 and 3. He had been born with an LV of 6. His own mother used to say he was born with predetermined cruelty, which sounds awful for a parent to say to their child, but she was completely right. 

She didn’t say it to be hurtful. She was a very kind monster, who helped teach him to control his emotions. As a young and angry child, he used to get into fights with the other children at the drop of a hat, so his mother took it upon herself to teach him methods to cope with his unusually high Level of Violence. By the time he was a teenager he had complete control over his… _disability_. 

For a while he had believed that being a pacifist was the only true way to live. 

And then the war happened.

After the war he lost some of that control, and his pacifistic ways had all but been destroyed. He became more prone to violent outbursts when angered, but he always made sure to extract himself from the presence of others if he knew he was going to have an episode. 

This hall had always been a toxic environment for him. 

Even before the DT experiments, other monsters had judged him openly whenever he passed through its golden interior. 

It had been quite a shock as a young monster walking through this beautiful hall and hearing other passing monsters whispering nasty things while looking down at him for his LV. 

He has been King Asgore’s right-hand man for a very long time, and as such, he had to pass through the Hall of Judgment rather frequently. It was the only way to reach the throne room. As one could imagine, there have been many unpleasant things spoken about him in this hall over the years. 

It didn’t take long for him to develop a kind of phobia of this place. 

Every time he entered the room his anxiety spiked because he was worried that someone was going to say something unpleasant or question him about his LV. 

That all changed once he started the DT experiments. 

Now when monsters happened to catch a glimpse of him while he was in the hall, they recoiled in fear at the sight of his LV. 

He absolutely _despised_ their fear. He’d rather have them spew hateful words from their ignorant mouths than have them quiver in fear for their lives. He was trying to help these wretched creatures with his research and they dared to show him such disrespect by acting as though he were some sort of psychotic killing machine! They didn’t know him. Most of the monsters that passed through the hall were wide-eyed, slack-jawed tourists. They didn’t know a damn thing. 

Recently he’s taken to loitering just outside the Hall of Judgement until there was a window of time where there were no monsters left in the hall. It was just better this way, less stress inducing.

Gaster peered into the long, golden hall. Today must be his lucky day because there wasn’t a soul in sight. Pulling the black pea coat he typically wore when he wasn’t at the lab tighter around himself, he set off down the hall at a brisk pace. The brown satchel slung over his shoulder that held all the paperwork for his meeting with Asgore, bounced against his hip as his pace increased slightly. He kept his eyes locked on the exit, least they stray to where he knew his LV was currently on display for all to see.

He didn’t want to look at it. 

The universe doesn’t take into account circumstance when dishing out Execution Points. Even killing in self-defense doesn’t stop an individual from gaining EXP. Life isn’t fair, but what else is new? 

Gaster’s soul pulsated rapidly in his chest during the entirety of his traversal through the magnificent hall. As soon as he reached the end and crossed over the threshold leading into the next room, the anxiety he felt while in the golden hall melted away and his soul stopped pounding against his ribs.

With that obstacle passed, Gaster continued to make his way towards the throne room. This small hall that led directly to the King’s Throne Room was always so eerily quiet. The sound of his boots against the stone flooring reverberated along the gray stone walls. 

He was halfway down the hall when he was startled by a scream that erupted from behind him that completely shattered the silence. 

“HALT, INTRUDER!”

Before Gaster even had time to turn around, his soul had turned green. Dropping his satchel, he tried pulling out of the green soul trap but found that his movements had become restricted. All he could do was change directions! 

The monster attacked without any hesitation. Spears were now flying at Gaster from every direction. Having been rooted to the spot with green magic, he couldn’t dodge. Quickly, he summoned a bone into his hand and began deflecting the oncoming spears left and right. 

Each time a magic spear was deflected by his bone, it dissipated instantly. By the end of the first wave of spears, Gaster had managed to gracefully deflect every single spear attack with impressive speed and accuracy. 

When the wave of spears ended, his soul returned to normal and he was able to move freely once more. Looking up, he saw a woman in heavy plate armor standing at the end of the hall hurtling spear after spear at him. 

The pattern of the spear attacks changed and Gaster was forced to drop his bone and go into a dodge roll to prevent the dangerous projectiles from skewering him. His lack of sleep must be catching up to him because the moment he pulled out of the roll, an achy throb of pain shot through his skull. The pain caused him to automatically clench his eye sockets shut, and momentarily drop to one knee. 

The armored woman must have spotted his fumble because when he reopened his eye sockets she was already barreling down on top of him, jabbing her crackling, blue magic spear towards his skull with a ferocious roar. 

Gaster summoned another bone into his skeletal hand and swung it in an upward arch. The bone collided with the spear knocking it, and its owner to the side. 

Gaster grinned. She was good, but she was far too impatient. 

He was about to strike her with the bone again when his soul turned green for a second time. Damn, the spears were now flying at him twice as fast! Gaster’s movements were a blur as he swung his bone 360 degrees around himself, deflecting each and every attack. Even the yellow spear attacks that tried to fool him by changing direction midair couldn’t penetrate his defenses. 

When the attack ended and his soul returned to normal once more, he stepped forward looking for his attacker. He had gotten turned around by the other attack and now he’s lost sight of-

“Hey nerd, deflect THIS!” 

He swung around to see the well-armored woman throw her blue magic spear with all her might directly towards him. Gaster just laughed and lazily stepped to the left. The spear harmlessly zipped past him. 

Seeing her last attack fail so spectacularly, the warrior became enraged and now she was charging full tilt towards the scientist. 

It was time to finish this. 

Gaster snapped his fingers and a purple hand shot forward. It formed a fist and sucker punched the woman right in the faceplate of her helmet. She stumbled backward and yelled, “Ow, shit!” More purple hands formed and now there was a barrage of fists striking her from every angle. “Ow. Ow! OW! Ngahhh! Get off of me!” she screeched as she swung her spear around wildly, trying to bat the hands away. 

Chuckling, Gaster stalked behind the distracted warrior. He materialized a bone into his hands and slid it over her head before pulling it tight against her throat, effectively cutting off her air. 

The woman gasped and now a new, fascinating, and intricate dance began. As the warrior struggled to get free, Gaster had to keep shifting his weight to prevent her from throwing him off of her. He pulled the bone tighter and now the woman was really running out of air and time. The woman’s struggling became much more frantic, but Gaster gave no indication of letting up.

It would be so easy to end her life like this. Gaster’s purple eyes flashed and he gripped the bone even tighter. 

Suddenly the woman stopped struggling. Her hand flew up to where he was gripping the bone and she began tapping his hand. It was an indication that she was done. 

Ah, this fight was already over… _Pity_.

The lights in his eyes returned to normal as the bone in his hand dissipated. The warrior woman fell to her hands and knees on the stone floor. 

Gaster strolled in front of the panting monster. Crossing his arms and smiling good-naturedly he said, “Good morning to you too, Undyne.”

The Captain of the Royal Guard sat cross-legged on the floor and pulled her helmet off, revealing a grinning fish woman. “Fuhuhuhu! Wow Doctor G, you really didn’t hold back today!” Gaster watched as she rubbed her neck. The lights in his eye sockets dimmed a little. “I’m sorry if I was too rough.” He really didn’t mean to get so aggressive with the young captain. He’s been exceptionally frustrated lately and he took it out on her without thinking. 

But the fish woman’s grin widened and her eyes sparkled in admiration. “Pfftt… Nah, that was great! I almost got you a few times.”

“Hmm… perhaps you _would_ have gotten a decent hit in if you hadn’t revealed your location when you threw that last spear.” 

Undyne laughed and said, “Yeah, I guess I got a little over zealous. Suppose I need a little more training, huh? I have to be in top shape if I’m going to crush any humans that get in my way.” 

Gaster really liked Undyne. Her anti-human convictions were most refreshing. He has noticed a disturbing increase in human sympathizers amongst the monster youth population in recent years. It was good to know that at least the leader of the Royal Guard had the right idea. She was also popular with the children so perhaps her views will rub off on them, which is for the best really. 

Gaster walked over to where his discarded satchel was laying and picked it up. He opened it and extracted the cinnamon bun he had purchased from the Snowdin Shopkeeper before coming here. 

“Here,” he said tossing the bun to the fish woman on the floor. She grabbed it out of the air with one hand and looked at it before saying, “Aw, rad! A fight with you _and_ a tasty Snowdin treat? Today has been totally awesome!” Only Undyne would consider getting her tailfin handed to her by an old skeleton as being something _totally awesome_. She shoved the gooey substance into her sharp, toothy mouth and leapt to her feet. 

“I have something else for you, or rather it’s from one of my coworkers. You remember Alphys from when you accompanied Asgore during his visit to the lab, correct?” Undyne thought for a moment before nodding enthusiastically. “Oh yeah, that chick seemed pretty cool.” 

Gaster pulled out several tapes of those strange cartoons his assistant liked to watch from his satchel and handed them to her. 

“Apparently you expressed interest in her movie collection and she wanted to lend you a few of them.” 

Most of the movies looked like typical fictional action packed adventure movies. One was called _Bleach_ , and the characters on the cover were wielding swords that were far too big for practical use. Was it called Bleach because the characters were so pale? Or perhaps did watching such a crappy cartoon make the viewers want to drink bleach? He made a mental note reminding him to ask Alphys. 

Just before he handed the last tape to Undyne, he happened to look at the back cover of one called _Strawberry Panic_ and saw two cartoon females engaging in rather risqué activities. Jesus Christ Alphys, could you lay it on any thicker? Gaster smirked. He was going to tease her mercilessly for this the next chance he gets. 

Undyne thanked Gaster for delivering the movies and told him to make sure to let Alphys know that she can’t wait to discuss these movies with her soon, and hopefully in person. Huh, Undyne seems really excited about these movies. Perhaps Alphys was onto something with this whole movie thing. He began to wonder what kind of movies Sans would enjoy… 

No, stop.

He was being stupid. So what, just because he slightly _cared_ about Sans, suddenly that meant he had to start gathering movies for them to bond over? That would be ridiculous. That was ridiculous… right? He cringed and grasped the front of his coat tightly. Why did his soul have to feel like it was in a vice every time he thought about his assistant? It made him feel sick and anxious. He didn’t understand these feelings at all. 

“Hey Doctor G, are you listening to me? Asgore is waiting for you in his throne room.”

Gaster tore his hand away from his chest and gave Undyne a nod of appreciation before walking into the throne room. 

The throne room was covered with golden flowers. It was so strange to see it like this. It didn’t use to be this way. Asgore’s gardening hobby only expanded to the throne room after Toriel left. 

In the thick of the golden flowers sat Asgore on his throne, pouring tea. In front of the boss monster was a little, white tea table with a matching white chair, which was no doubt meant for him. 

When Asgore noticed Gaster, he waved cheerfully at the skeleton and said in a booming voice, “Gaster my friend, please take a seat.” The large goat monster gestured to the small, white chair.

Gaster trudged through the golden flowers, not caring in the slightest if they were crushed beneath his black boots. If Asgore cared, he didn’t show it. He just continued to smile politely as he waited for his old skeleton friend to take a seat. 

When Gaster was standing directly in front of Asgore, he bowed. “It’s good to see you, Sire,” he said in a tone befitting any servant of the King. Asgore’s smile broadened. “Must you always be so formal, my friend?” He asked. Gaster didn’t say anything. He just dropped into the seat provided for him and pulled his notepad out of his satchel. 

Asgore held up a hand and said, “Before we begin our meeting I wanted to give you something.” He pushed a mug towards Gaster, who picked it up and examined it with intrigue.

Printed on the mug were the words:

I LIKE MY COFFEE HOW I LIKE MY BLACK HOLES 

DARK AND DENSE

Gaster withheld a cringe. If only Asgore knew what was actually at the center of the Core, then perhaps he would not have gotten him such a mug. Gaster looked up and flashed Asgore his best fake smile. “Very clever, Sire.” 

Asgore beamed and said, “I knew you’d like it, you always did like that science stuff.”

 _Science stuff indeed_! Gaster just nodded and once again displayed a fake smile. “If it’s alright with his majesty, I would like to begin discussing the different projects we’ve been working on at the Laboratory this month.”

Asgore waved his hand in a way that suggested that Gaster was allowed to continue.

As Gaster spoke at great lengths about the Core, the various projects at the lab, and everything else that needed to be coved at these monthly meetings, Asgore drank his tea an nodded his head politely at every moment it seemed appropriate to do so. It was clear Asgore had zero idea what half of what he said meant. It always kind of ticked him off that Asgore hardly ever asked questions when he didn’t understand something. How was he supposed to learn if he didn’t bother to ask questions when he became confused? It honestly felt like Asgore was just humoring him by allowing him to talk about the progress of his science division. 

Exasperated by Asgore’s lack of interest, Gaster quickly finished up the progress report and dropped the notepad back into his satchel. 

Here came the hard part. Gaster took a sip from his own mug and said, “Asgore, there’s something else I need to discuss with you.” The use of the King’s first name had the boss monster perking up already. Frowning, Asgore said, “Golly, you look awfully tense. Is everything alright, Gaster?” The scientist gave a stiff nod and said, “The other day I was forced the break the royal promise I made that forbid me from discussing the falling down illness and DT,” he confessed. 

Asgore looked surprised but he didn’t appear angry. “Why did you break the promise, my friend? I thought you said we needed to keep this all a secret so that the public wouldn’t find out and panic.” 

“Due to an… um, _accident_ that happened at the lab, I found that it became necessary for me to tell my newest assistant, Sans, about our efforts to cure the falling down illness. I’m sorry Sire, it’s entirely my fault.” Gaster went on to tell Asgore about his continued use of DT on himself, despite the fact that Asgore had specifically told him not do anymore DT experiments on monsters. He didn’t go into specifics about how the DT was affecting him, but he did tell Asgore that it caused him some mild mood swings that made him lash out at Sans. 

It was a lie of course. What was happening to him was beyond just mood swings, but the King simply wouldn’t be able to understand if he had told him that the DT substance was actually periodically influencing and even controlling his actions. He knew that the information would only frighten Asgore, and that something he absolutely didn’t want. So yes, he lied.

By the end of his explanation Asgore was looking rather concerned. “I wish you wouldn’t have gone against my wishes by continuing with the DT experiments,” Asgore said with disappointment clearly evident in his voice. Gaster wasn’t surprised. He knew Asgore would be disappointed. “I would also just like to say that if you believe Sans is capable of helping you with the epidemic, then I wish you two the best of luck. I know things have been hard since you last assistant stepped down, but maybe this new assistant of yours will provide you with a good change of pace.”

Gaster gave Asgore a real smile this time and said, “yes, I think Sans will provide a fresh new perspective on the illness and will become a valuable asset to my research.” 

“Excellent,” Asgore boomed merrily. “As long as you’ve stopped taking those terrible tablets and you do your best to find a cure for this illness, then all is forgiven!” Gaster took a sip from his mug. Just a few minutes ago he had been pissed at Asgore for his lack of questions when he gave his monthly report, and now he was praising the gods that the King didn’t ask too many questions. It would have been extremely difficult to explain to Asgore exactly what he put his assistant through. 

Gaster nearly spit out his tea when a large, paw-like hand covered the hand he had been resting on the white tea table. Asgore leaned over with his hand still on top of his own and whispered in a deeper, huskier voice, “Now tell me. How are you _really_ doing, Gaster?” 

Oh.

Oh. It was going to be one of _those_ days.

The lights in Gaster’s eye sockets narrowed. “I’m doing just fine, Sire,” he said cautiously as he slowly tried sliding his hand out from under Asgore’s. The boss monster just tightened his grip and now the King’s other hand was resting against his face. 

“Really? Because you look awfully tired. Why don’t you come and rest with me?” 

The implication of those words hung heavy in the air.

Gaster immediately jerked himself out of his King’s grasp and hissed, “Stop it, Asgore.”

Hurt flashed across Asgore’s face. He said, “I-I’m sorry Gaster, I’ve just really missed you.” 

Gaster shot a glare up at the large goat monster, but he quickly lowered his gaze and shook his head. “No. No Asgore, you don’t miss me. You miss Toriel. You miss your wife,” he stated firmly. Gaster knew Asgore was just confused. The death of his children and being abandoned by Toriel has taken its toll on the boss monster. He just wasn’t thinking straight. 

Asgore frowned and said, “We used to have so much fun together. Don’t you remember how after the war, when you just got out of the hospital, we explored this whole area together?” He was staring off into the distance, clearly remember a different time. 

“Yes, and as I recall while I was documenting the local flora, you were trying to find the perfect plant to make tea with,” Gaster said tightly. Those _were_ good memories, but that was in the past. God, he really couldn’t stand it when Asgore got like this. 

“Why can’t we be like that again? Don’t you still hold feelings for me?”

Ah… and there it was! The million dollar question that Gaster loathed to answer.

Getting increasingly more upset, Gaster clenched his fists by his side and said through gritted teeth, “I think you made your feelings for _me_ quite clear when you chose Toriel over myself!” He was having a very difficult time keeping the anger he felt out of his voice. 

It’s true that there may have been a point in time when he truly loved Asgore. 

During the Human and Monster War, Asgore had saved him from the humans. The young King had even carried him to a safe location to be treated for his injuries. After that, Asgore came to visit him in the hospital every chance he got and they quickly became thick as thieves. It wasn’t long until their feeling for each other grew into something more.  
They were young, passionate, and naïve. He supposed they both knew it couldn’t last, but at the time, it seemed like it would go on forever. 

“Wingdings…” the King gave his scientist a pleading look, but Gaster was having none of it. “Don’t _Wingdings_ me, Asgore. Look, I understand! A King needed a Queen, right? Not some lanky, antisocial, scientist by his side!” Gaster’s usual calm and collected attitude had been completely thrown out the window by this point. He could feel his anger fluctuating dangerously. He needed to leave.

Bolting out of his chair, he threw on his coat and slung his satchel over his shoulder. He turned to leave when Asgore rose from his throne.

“Gaster, wait. Please! I’m sorry. I’m sorry that I was foolish enough to believe that things could go back to the way they were before… before you know.”

Before _Toriel_ was what Asgore was implying. Gaster actually really liked Toriel and he respected her. She wasn’t to blame for any of this. Asgore had just reached a point in his life where he needed to settle down and sire a few heirs. It was expected of him, and Toriel was perfect for Asgore.

Asgore and Toriel were in love and he was happy for them. He was Asgore’s best man at their wedding and he even managed to keep a smile on his face through the whole ordeal. He waited patiently to have his breakdown alone like the heartbroken loser that he was. Sure it hurt, but he hastily convinced himself his feelings were illogical and irrational. Perhaps he grew a little colder in doing so, but it was necessary. At the time, he was finishing the last touches to his design of the Core and he needed to focus. 

As the years progressed, the pain dulled. Of course as soon as Gaster felt okay with the situation, that’s when Asgore came to him looking for comfort. He should have turned Asgore away, but he was his King and he was in pain. He could not find it in himself to turn his friend away. The King had been having a difficult time keeping moral high in his kingdom, and he and Toriel were having issues conceiving a child. 

So yes, he and Asgore had engaged in a few illicit affairs. 

That had been a mistake. The moment Toriel announced she was with child, he and Asgore vowed to end their relationship permanently. Gaster once again ended up feeling hurt with the addition of feeling used. He wasn’t going to make that mistake again.

Turning to his King, Gaster said, “Yes, you are a fool for thinking that things could just go back to how they were. We made a promise before you had your first child and I intend to keep it.” Gaster started walking towards the door.

“STOP!” Asgore’s bellow rang throughout the entire throne room.

Gaster stopped in his tracks and glared over his shoulder at the boss monster. “Is that an _order_ , Sire?” Asgore physically recoiled at Gaster’s words. “No! You know I would never use my position as King to force you to do anything you didn’t want to do!” 

Gaster’s eye sockets widened and he turned around sharply to face Asgore properly. 

“Now we both know that’s a lie,” Gaster growled. His tone had become low and dangerous. “I do believe it was you who ordered me to destroy all those monsters, was it not?”  
Before Asgore could answer, Gaster turned and walked out into the hall, slamming the throne room door in the distressed boss monster’s face.

**Notes for the Chapter:**

> .  
> ..  
> ...
> 
> OMG! ASGORE WANTED GASTER'S ASS-TER BLASTER IF YA KNOW WHAT I MEAN. *Aggressive eyebrow wiggling*
> 
> *cough* Sorry about that... I guess I should tag this as implied Kingdings... ah well, I'll do that later.
> 
> So... bonus points for anyone who knows what's so important about this sentence: _But the fish woman’s grin widened and her eyes sparkled in admiration._
> 
> I'm sure if you think about Undyne's character you'll figure it out pretty quickly.
> 
> Also my Tumblr is: https://www.tumblr.com/blog/shadowmelter
> 
> Submit drawing of Gaster to me, yo! Even if it's not my Gaster or if you think you suck at drawing. I wanna see him!
> 
> Completely self indulgent, but headcannon for Gaster's voice would be Ultron from Avengers: Age of Ultron. Sophisticated, yet crazy.


End file.
